Producing C5 olefins from steam cracker C5 feeds

ABSTRACT

Producing C5 olefins from steam cracker C5 feeds may include reacting a mixed hydrocarbon stream comprising cyclopentadiene, C5 olefins, and C6+ hydrocarbons in a dimerization reactor where cyclopentadiene is dimerized to dicyclopentadiene. The dimerization reactor effluent may be separated into a fraction comprising the C6+ hydrocarbons and dicyclopentadiene and a second fraction comprising C5 olefins and C5 dienes. The second fraction, a saturated hydrocarbon diluent stream, and hydrogen may be fed to a catalytic distillation reactor system for concurrently separating linear C5 olefins from saturated hydrocarbon diluent, cyclic C5 olefins, and C5 dienes contained in the second fraction and selectively hydrogenating C5 dienes. An overhead distillate including the linear C5 olefins and a bottoms product including cyclic C5 olefins are recovered from the catalytic distillation reactor system. Other aspects of the C5 olefin systems and processes, including catalyst configurations and control schemes, are also described.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application, pursuant to 35 U.S.C. § 119(e), claims benefit to U.S.Provisional Application Ser. Nos. 62/109,263, 62/109,272, 62/109,279,and 62/109,289, all of which were filed Jan. 29, 2015. Theseapplications are incorporated herein by reference in their entirety.

BACKGROUND

Crude streams for the commercial production of olefins contain variouscompounds as impurities. Acetylenic and diene impurities need to beremoved from the streams to produce acceptable quality olefin products.To produce olefins such as ethylene, propylene, butene, pentene and thelike, acetylenic impurities such as acetylene, methyl acetylene, vinylacetylene, ethyl acetylene, 2-methyl-1-buten-3-yne and the like, as wellas diene compounds, such as butadiene, propadiene, and the like, invarious crude mixed C2-C5 streams need to be removed with minimum lossof useful materials such as ethylene, propylene, butene, pentene, andthe like in the feed streams. The preferred technique for thepurification in commercial practice is the selective hydrogenation ofacetylenic and diene compounds over hydrogenation catalysts.

Crude C5 olefin-containing streams may include various dienes andacetylenes, which often must be removed before use of the C5olefin-containing stream in downstream processing units, such as adownstream metathesis unit. In addition to the need to remove dienes andacetylenes, which produce coke and shorten metathesis catalyst runlength, cyclopentene must also be removed from the C5 feed to a very lowlevel, such as less than 0.5 wt %, 1.5 wt %, or 2.5 wt %, ascyclopentene may undergo undesirable ring-opening metathesispolymerization in the downstream metathesis unit.

Various feeds may be used to provide the C5 olefins, including C5fractions from crackers, such as a fluid catalytic cracker (FCC) or asteam cracker. The mixed C5's from such crackers is typically processedto result in feed of only the desired C5's, with minimal impurities, tothe metathesis unit. For example, C5's from an FCC unit may be fed to aselective hydrogenation unit and fractionated to separate the C6+hydrocarbons and cyclic C5 olefins from linear and iso C5 olefins, whichmay then be used in a metathesis process.

Such a simple system may not be suitable for steam cracker C5 products,however. Steam cracking processes produce C5 hydrocarbon streams havinga very high concentration of cyclopentadiene and dicyclopentadiene, inaddition to linear C5 dienes, isoolefins, and acetylenes, relative toFCC C5 products. The higher diene content, for example, if processedsimilar to an FCC C5 product, may result in high rates of catalystfouling and potential runaway reactions. Further, sulfur compoundspresent in the C5 feed could potentially inhibit/damage the catalystperformance.

U.S. Pat. No. 3,492,220 to Lempert et al., 1970, disclosed a process forhydrotreating a full boiling-range pyrolysis gasoline containing styreneand C5 and lighter hydrocarbons with a sulfided nickel catalyst underconditions that produce either stable gasoline in a single zone or asubstantially olefin-free, sulfur-free product in two or more reactionzones. However, this disclosed process is not selective to olefins.

U.S. Pat. No. 3,691,066 to Carruthers et al., 1972, disclosed asupported nickel catalyst for selective hydrogenation of unsaturatedgasolines, e.g. steam cracker gasoline. The diene content is reducedfrom 4-55% wt to below 0.5% wt. Total sulphur content of the feedstockis 0.1-1.5% wt., of which 0.003-1.0% wt. may be thiophenic sulphur. Runsof over 500 hours, particularly over 1000 hours were noted are possible.It was stated therein that fresh wholly elemental nickel catalyst is notselective in its hydrogenation activity and will hydrogenate mono anddiolefins and aromatics and the fact that monoolefins and aromaticsremain unhydrogenated in the present process is due to the partialsulphiding of the nickel catalyst by the thiophenic sulphur normallypresent in the feedstock.

U.S. Pat. No. 4,059,504 to Bauer, 1977, disclosed a process in whichpyrolysis gasoline is stabilized by hydrotreating in the presence of acatalyst of cobalt-tungsten sulfide supported on high surface areaalumina. It was stated in this patent that the non-noble catalysts, themost widely used being Ni, W—Ni, Ni—Mo and Co—Mo, supported on ahigh-surface alumina base, require either pre-sulfidation or operationwith high sulfur content feeds. It was also noted that the non-noblemetal catalysts heretofore used in the art have the disadvantage in thatthey tend to produce polymers during the hydrotreating. In this patent,the active form of the catalyst is the sulfide form, and the catalyst ispreferably pre-sulfided, although when using high sulfur feeds, theactive sulfide form is produced on-stream, whereby, in some cases,pre-sulfiding is not required.

EP0011906 to Christy et al., 1983, disclosed a process for the selectivehydrogenation of dienes in pyrolysis gasoline which includes catalytichydrogenation of the pyrolysis gasoline in at least three consecutivereactors. In at least two of the consecutive reactors, the processincludes recirculating part of the hydrocarbon mixture emerging from areactor over that reactor. The catalyst used for the catalytichydrogenation comprises partially sulfided nickel on alumina as asupport. The weight ratio of hydrocarbon mixture recirculated to thefirst reactor and the pyrolysis gasoline fed thereto is from 5 to 15 andto the second reactor from 2 to 4. The examples provided show theunsaturate recovery (dienes+olefins) for the first case is 91.27% andfor the second case is 87.79%, with 5000 dienes ppm remaining in theproduct stream.

U.S. Pat. No. 6,686,309 ('309) to Didillon et al, 2004, disclosed apalladium based catalyst, with at least one metal selected frommolybdenum and tungsten, in the form of at least one oxide, forselective hydrogenation of unsaturated diolefinic compounds in gasolineswithout hydrogenating the aromatic and mono-olefinic compounds. In thebackground of the '309 patent, it was acknowledged that two main typesof catalyst are generally used for hydrogenating diolefins and styreniccompounds: catalysts using noble group VIII metals such as palladium,and those using non-noble group VIII metals such as nickel. It wasstated that the second type of catalyst generally has a lower activityand undesired oligomerizing properties, which necessitates frequentregeneration and the use of a distillation column after hydrogenation toeliminate the heavy compounds. Further, such catalysts were noted asuseful to only treat feeds containing large quantities of mercaptans,such as that found in catalytic cracking gasolines.

CN101254465 A (Sinopec) disclosed a selective hydrogenation catalyst forcracking C5 streams, which contains the following components in thegiven mass percentages: Ni 10-35%, La 0.5-3%, Ag 0.3-3% and aluminumoxide carrier 59-89.2%, and can contain other metals. Metal La andprecious metal Ag are claimed to be required to improve catalystselectivity and resistance to carbon deposition. It is stated that sincecracking C5 fraction containing a lot of dienes is easy to generate apolymer which will cover the active sites of the catalyst and reducecatalyst activity, adding an alkaline or alkaline earth metal catalystwill be good to reduce the formation of polymers.

SUMMARY OF THE CLAIMED EMBODIMENTS

Embodiments disclosed herein relate generally to processes and systemsfor the production of linear C5 olefins from steam cracker C5 feeds. Theprocesses and systems disclosed herein have been found useful fortreating and separating steam cracker C5 hydrocarbons such that theolefins recovered from the steam cracker C5 hydrocarbons may be used indownstream processes, such as in a downstream metathesis unit for theproduction of propylene, for example.

In one aspect, embodiments disclosed herein relate to a process forproducing C5 olefins from a steam cracker C5 feed. The process mayinclude reacting a mixed hydrocarbon stream comprising cyclopentadiene,linear C5 olefins, cyclic C5 olefins, and C6+ hydrocarbons whereincyclopentadiene is dimerized to form dicyclopentadiene. The reactedmixture may then be separated in a fractionator to form a first fractioncomprising the C6+ hydrocarbons and dicyclopentadiene and a secondfraction comprising the linear and cyclic C5 olefins and C5 dienes. Thesecond fraction and hydrogen may then be fed to a catalytic distillationreactor system, wherein the second fraction is introduced intermediate afirst catalyst zone and a second catalyst zone. Concurrently in thecatalytic distillation reactor system: the linear C5 olefins areseparated from the cyclic C5 olefins and C5 dienes contained in thesecond fraction; and at least a portion of the C5 dienes are selectivelyhydrogenated to form additional C5 olefins. An overhead distillateincluding the linear C5 olefins and a bottoms product including cyclicC5 olefins are recovered from the catalytic distillation reactor system.

In another aspect, embodiments disclosed herein relate to a process forproducing C5 olefins from a steam cracker C5 feed. The process mayinclude reacting a mixed hydrocarbon stream comprising cyclopentadiene,linear C5 olefins, cyclic C5 olefins, and C6+ hydrocarbons in adimerization reactor wherein cyclopentadiene is dimerized to formdicyclopentadiene, producing a dimerization reactor effluent. Thedimerization reactor effluent may then be separated in a fractionator toform a first fraction comprising the C6+ hydrocarbons anddicyclopentadiene and a second fraction comprising the linear and cyclicC5 olefins and C5 dienes. The second fraction, a saturated hydrocarbondiluent stream, and hydrogen may then be fed to a catalytic distillationreactor system, wherein the second fraction is introduced intermediate afirst catalyst zone and a second catalyst zone. Concurrently in thecatalytic distillation reactor system: the linear C5 olefins areseparated from the saturated hydrocarbon diluent, the cyclic C5 olefins,and C5 dienes contained in the second fraction; and at least a portionof the C5 dienes are selectively hydrogenated to form additional C5olefins. An overhead distillate including the linear C5 olefins and abottoms product including cyclic C5 olefins are recovered from thecatalytic distillation reactor system.

The process may further include: purging a portion of the bottomsproduct; reacting a remaining portion of the bottoms product in a totalhydrogenation unit to convert the cyclic C5 olefins to cyclopentane; andrecycling the cyclopentane to the catalytic distillation reactor systemas the saturated hydrocarbon diluent. In some embodiments, the saturatedhydrocarbon diluent may include one or more hydrocarbons having a normalboiling point of at least 102.5° F.

The process may also include feeding the overhead distillate from thecatalytic distillation reactor system to a metathesis unit andconverting the linear C5 olefins to propylene. The overhead distillatemay include less than 2.5 wt % cyclopentene, and the second fraction mayinclude less than 0.5 wt % benzene, in various embodiments. An olefinrecovery, measured as moles linear and branched C5 olefins in theoverhead distillate divided by moles linear and branched C5 olefins anddienes in the mixed hydrocarbon stream, may be greater than 80%, such asgreater than 83%.

The process may include, in various embodiments: operating thedimerization reactor at a pressure in the range from about 130 psia toabout 170 psia and a temperature in the range from about 210° F. toabout 250° F.; operating the fractionator at a pressure in the rangefrom about 15 psia to about 85 psia and at a condenser temperature inthe range from about 97° F. and 213° F.; operating the catalyticdistillation reactor system at a pressure in the range from about 60psia to about 240 psia and a reboiler temperature in the range from 220°F. and 320° F., and a hydrogen partial pressure in the range from about1 psi to about 25 psia; and operating the total hydrogenation unit at apressure in the range from about 220 psia to about 300 psia and at atemperature in the range from about 200° F. and 260° F.

The mixed hydrocarbon stream may also contain sulfur compounds, whichmay be recovered in the first fraction. The process may also includepartially vaporizing the second fraction prior to introducing the secondfraction to the catalytic distillation reactor system. The partialvaporizer may be operated at conditions sufficient to vaporize between 5wt % and 95 wt % of the C5 dienes. In other embodiments, the processfurther includes separating the overhead distillate to recover a productfraction comprising linear C5 olefins and a recycle fraction comprisingcyclopentene.

In another aspect, embodiments disclosed herein relate to a process forproducing C5 olefins from a steam cracker C5 feed. The process mayinclude reacting a mixed hydrocarbon stream comprising cyclopentadiene,linear C5 olefins, cyclic C5 olefins, and C6+ hydrocarbons in adimerization reactor wherein cyclopentadiene is dimerized to formdicyclopentadiene, producing a dimerization reactor effluent. Thedimerization reactor effluent may then be separated in a fractionator toform a first fraction comprising the C6+ hydrocarbons anddicyclopentadiene and a second fraction comprising the linear and cyclicC5 olefins and linear C5 dienes. The second fraction, a saturatedhydrocarbon diluent stream, and hydrogen are fed to a catalyticdistillation reactor system, wherein the second fraction is introducedbelow a first catalyst zone. Concurrently in the catalytic distillationreactor system: the linear C5 olefins are separated from the saturatedhydrocarbon diluent, the cyclic C5 olefins, and linear C5 dienescontained in the second fraction; and at least a portion of the C5dienes are selectively hydrogenating to form additional linear C5olefins. An overhead distillate including the linear C5 olefins and abottoms product including cyclic C5 olefins are recovered from thecatalytic distillation reactor system.

The process may further include purging a portion of the bottomsproduct; reacting a remaining portion of the bottoms product in a totalhydrogenation unit to convert the cyclic C5 olefins to cyclopentane; andrecycling the cyclopentane to the catalytic distillation reactor systemas the saturated hydrocarbon diluent. In some embodiments, the processfurther includes feeding the second fraction to a fixed bed selectivehydrogenation unit to selectively hydrogenate C5 dienes prior to feedingthe second fraction to the catalytic distillation reactor system. Thesecond fraction may be partially vaporized prior to introducing thesecond fraction to the catalytic distillation reactor system, and theoverhead distillate may be separated to recover a product fractioncomprising linear C5 olefins and a recycle fraction comprisingcyclopentene.

In another aspect, embodiments disclosed herein relate to a process forproducing C5 olefins from a mixed C5 feed. The process may includefeeding hydrogen and a mixed hydrocarbon stream comprisingcyclopentadiene, linear C5 olefins, cyclic C5 olefins, and C6+hydrocarbons to a catalytic distillation reactor system. Concurrently inthe catalytic distillation reactor system: the linear C5 olefins areseparated from the cyclic C5 olefins, C5 dienes, and C6+ hydrocarbons;and at least a portion of the C5 dienes are selectively hydrogenating toform additional linear C5 olefins. A liquid side draw is withdrawn froma stage below a mixed hydrocarbon feed location and a hydrogen feedlocation and above a main reboiler, at least partially vaporizing theliquid side draw in an intermediate reboiler, and returning the at leastpartially vaporized liquid side draw to the catalytic distillationreactor system. An overhead distillate including the linear C5 olefinsand a bottoms product including cyclic C5 olefins are recovered from thecatalytic distillation reactor system. In some embodiments, the mainreboiler of the catalytic distillation reactor system may be operated ata temperature of less than about 302° F.

In another aspect, embodiments disclosed herein relate to a process forthe selective hydrogenation of C5 dienes in a mixed C5 hydrocarbonstream. The process may include feeding hydrogen and a C5-olefincontaining stream containing linear pentenes, dienes, acetylenes, and adiluent compound to a catalytic distillation reactor system.Concurrently in the catalytic distillation reactor system, theacetylenes and dienes may be hydrogenated, and the C5-olefin containingstream may be fractionated to recover an overheads fraction comprisingthe pentenes and a bottoms fraction. The catalytic distillation reactorsystem may have at least three reaction zones, including: a firstreaction zone disposed below a C5-olefin containing stream feedelevation and containing a nickel-based catalyst; a second reaction zonedisposed above the C5-olefin containing stream feed elevation andcontaining a nickel-based catalyst; and a third reaction zone disposedabove the second reaction zone and containing a palladium-basedcatalyst.

In another aspect, embodiments disclosed herein relate to a process forproducing C5 olefins from a steam cracker C5 feed. The process mayinclude reacting a mixed hydrocarbon stream comprising cyclopentadiene,linear C5 olefins, cyclic C5 olefins, and C6+ hydrocarbons in adimerization reactor wherein cyclopentadiene is dimerized to formdicyclopentadiene, producing a dimerization reactor effluent. Thedimerization reactor effluent may then be separated in a fractionator toform a first fraction comprising the C6+ hydrocarbons anddicyclopentadiene and a second fraction comprising the linear and cyclicC5 olefins and C5 dienes. The second fraction, a saturated hydrocarbondiluent stream, and hydrogen may be fed to a catalytic distillationreactor system, which may have at least three reaction zones, includinga first reaction zone disposed below a C5-olefin containing stream feedelevation and containing a nickel-based catalyst, a second reaction zonedisposed above the C5-olefin containing stream feed elevation andcontaining a nickel-based catalyst, and a third reaction zone disposedabove the second reaction zone and containing a palladium-basedcatalyst. Concurrently in the catalytic distillation reactor system: thelinear C5 olefins may be separated from the saturated hydrocarbondiluent, the cyclic C5 olefins, and C5 dienes contained in the secondfraction, and at least a portion of the C5 dienes may be selectivelyhydrogenated to form additional C5 olefins. An overhead distillateincluding the linear C5 olefins may be recovered from the catalyticdistillation reactor system. A bottoms product including cyclic C5olefins may also be recovered from the catalytic distillation reactorsystem.

The process may further include: purging a portion of the bottomsproduct; reacting a remaining portion of the bottoms product in a totalhydrogenation unit to convert the cyclic C5 olefins to cyclopentane; andrecycling the cyclopentane to the catalytic distillation reactor systemas the saturated hydrocarbon diluent. The saturated hydrocarbon diluentmay be one or more hydrocarbons having a normal boiling point of atleast 102.5° F. The process may also include feeding the overheaddistillate from the catalytic distillation reactor system to ametathesis unit and converting the linear C5 olefins to propylene.

In some embodiments, the overhead distillate may contain less than 2.5wt % cyclopentene, and the second fraction may contain less than 0.5 wt% benzene. An olefin recovery, measured as linear and branched C5olefins in the overhead distillate divided by linear and branched C5olefins and dienes in the mixed hydrocarbon stream, may be greater than92.5 wt %, such as greater than 95 wt %.

The process may include: operating the dimerization reactor at apressure in the range from about 130 psia to about 170 psia and atemperature in the range from about 210° F. to about 250° F.; operatingthe fractionator at a pressure in the range from about 15 psia to about85 psia and at a condenser temperature in the range from about 97° F.and 213° F.; operating the catalytic distillation reactor system at apressure in the range from about 60 psia to about 240 psia and areboiler temperature in the range from 220° F. and 320° F., and ahydrogen partial pressure in the range from about 1 psi to about 25psia; and operating the total hydrogenation unit at a pressure in therange from about 220 psia to about 300 psia and at a temperature in therange from about 200° F. and 260° F. The process may further includeseparating the overhead distillate to recover a product fractioncomprising linear C5 olefins and a recycle fraction comprisingcyclopentene.

The nickel-based catalyst may contain from about 5 wt % to about 30 wt %nickel. The nickel-based catalyst may be disposed on a diatomaceousearth support, have a BET surface area in the range from about 20 m²/gto about 400 m²/g, and have a pore volume in the range from about 0.2ml/g to about 0.7 ml/g. The palladium-based catalyst may contain fromabout 0.2 to about 1.0 wt % palladium disposed on an alumina support.

In another aspect, embodiments disclosed herein relate to a system forproducing C5 olefins from a mixed C5 hydrocarbon feedstock. The systemmay include a catalytic distillation reactor system for concurrentlyconverting C5 dienes to C5 olefins and separating the mixed C5hydrocarbon feedstock into an overheads olefin product and a bottomsproduct. The catalytic distillation reactor system may have at leastthree reaction zones, including: a first reaction zone disposed below aC5-olefin containing stream feed elevation and containing a nickel-basedcatalyst; a second reaction zone disposed above the C5-olefin containingstream feed elevation and containing a nickel-based catalyst; and athird reaction zone disposed above the second reaction zone andcontaining a palladium-based catalyst.

The system may further include: a dimerization reactor for convertingcyclopentadiene in a mixed hydrocarbon to dicyclopentadiene andproducing a dimerization reactor effluent; and a separator forseparating the dimerization reactor effluent to form a bottoms fractionincluding the dicyclopentadiene and an overheads fraction comprising themixed C5 hydrocarbon feedstock. The system may also include a totalhydrogenation reactor for converting cyclopentene in the bottoms productto cyclopentane. A flow conduit may also be provided for recycling aneffluent from the total hydrogenation reactor to the catalyticdistillation reactor system.

In another aspect, embodiments disclosed herein relate to a process forthe selective hydrogenation of C5 dienes in a mixed C5 hydrocarbonstream. The process may include: feeding hydrogen and a C5-olefincontaining stream comprising linear pentenes, dienes, acetylenes, and adiluent compound to a catalytic distillation reactor system.Concurrently in the catalytic distillation reactor system, theacetylenes and dienes may be hydrogenated, and the C5-olefin containingstream may be fractionated to recover an overheads fraction comprisingthe pentenes and a bottoms fraction. The process may further includedetermining a concentration of the diluent compound at one or morecolumn elevations, and adjusting one or more column operating parametersto maintain a set point concentration or a concentration profile of thediluent compound at the one or more column elevations.

The catalytic distillation reactor system may include an upper catalystzone above a C5-olefin containing stream feed elevation and a lowercatalyst zone below the C5-olefin containing stream feed elevation. Theprocess may further include at least one of: measuring a concentrationof the diluent compound at an elevation below the lower catalyst zone;measuring a concentration of the diluent compound at an elevationintermediate the upper and lower catalyst zones; or measuring aconcentration of the diluent compound at an elevation above the uppercatalyst zone. Alternatively or additionally, the process may include atleast one of: measuring a density of a liquid fraction at an elevationbelow the lower catalyst zone and determining the concentration of thediluent compound at the elevation below based upon the measured density;measuring a density of a liquid fraction at an elevation intermediatethe upper and lower catalyst zones and determining the concentration ofthe diluent compound at the elevation intermediate based upon themeasured density; or measuring a density of a liquid fraction at anelevation above the upper catalyst zone and determining theconcentration of the diluent compound at the elevation above based uponthe measured density.

The diluent compound may include cyclopentane, cyclopentene, or acombination thereof. In some embodiments, the diluent compound comprisesone or more hydrocarbons having a normal boiling point in the range fromabout 100° F. to about 125° F. In various embodiments, the diluentcompound comprises one or more hydrocarbons having a specific gravity inthe range from about 0.7 to about 0.8.

In some embodiments, a sample elevation (the elevation at which a sampleis withdrawn from the column) used in the determining step is disposedproximate an elevation of maximum rate of change in concentration of thediluent compound within the catalytic distillation reactor system. Theprocess may further include determining an elevation of maximum rate ofchange in concentration of the diluent compound within the catalyticdistillation reactor system.

The adjusting step may include at least one of: decreasing an overheadflow and increasing a reflux flow when a diluent compound concentrationprofile starts to move up the column and the reflux flow is below acolumn flooding value; increasing an overhead flow and decreasing refluxflow when a diluent compound concentration profile starts to move downthe column and the reflux flow is above a minimum design value;decreasing a reboiler duty and an overhead flow when the diluentcompound concentration profile starts to move up the column; orincreasing a reboiler duty and an overhead flow when the diluentcompound concentration profile starts to move down the column.

In another aspect, embodiments disclosed herein relate to a process forthe selective hydrogenation of C5 dienes in a mixed C5 hydrocarbonstream. The process may include: feeding hydrogen and a C5-olefincontaining stream comprising linear pentenes, dienes, acetylenes,cyclopentane and cyclopentene to a catalytic distillation reactorsystem, and concurrently in the catalytic distillation reactor system:hydrogenating the acetylenes and dienes, and fractionating the C5-olefincontaining stream. An overheads fraction comprising the pentenes may berecovered from the catalytic distillation reactor system, as may be abottoms fraction. The process may also include determining a density ofa liquid fraction at one or more column elevations, and adjusting one ormore column operating parameters to maintain a set point density ordensity profile at the one or more column elevations.

The catalytic distillation reactor system may include an upper catalystzone above a C5-olefin containing stream feed elevation and a lowercatalyst zone below the C5-olefin containing stream feed elevation. Insuch embodiments, the process may include at least one of: measuring adensity of the liquid fraction at an elevation below the lower catalystzone; measuring a density of the liquid fraction at an elevationintermediate the upper and lower catalyst zones; or measuring a densityof the liquid fraction at an elevation above the upper catalyst zone.The process may further comprising estimating a concentration of atleast one of cyclopentene and cyclopentane in the liquid fraction(s)based upon the measured density(ies).

The adjusting may include at least one of: decreasing an overhead flowand increasing a reflux flow when a density profile indicates aconcentration of a target compound is starting to move up the column andthe reflux flow is below a column flooding value; increasing an overheadflow and decreasing reflux flow when a density profile indicates aconcentration of a target compound is starting to move down the columnand the reflux flow is above a minimum design value; decreasing areboiler duty and an overhead flow when the density profile indicates aconcentration of a target compound is starting to move up the column; orincreasing a reboiler duty and an overhead flow when the density profileindicates a concentration of a target compound is starting to move downthe column. The target compound may include cyclopentane, cyclopentene,or a combination thereof. The diluent compound may include one or morehydrocarbons having a normal boiling point in the range from about 100°F. to about 125° F., and in some embodiments the diluent compoundcomprises one or more hydrocarbons having a specific gravity in therange from about 0.7 to about 0.8.

In another aspect, embodiments disclosed herein relate to a method forcontrolling a catalytic distillation reactor system, including: feedingone or more reactants and an inert compound to a catalytic distillationreactor system having one or more reaction zones; concurrently in thecatalytic distillation reactor system: converting the reactants to oneor more products; and fractionating the reactants and products;recovering an overheads fraction; recovering a bottoms fraction. Aconcentration of the inert compound may be determined at one or morecolumn elevations, and one or more column operating parameters may beadjusted to maintain a set point concentration or a concentrationprofile of the inert compound at the one or more column elevations.

In another aspect, embodiments disclosed herein relate to a system forproducing C5 olefins from a mixed C5 hydrocarbon feedstock. The systemmay include: a catalytic distillation reactor system, including one ormore reaction zones, for concurrently converting C5 dienes to C5 olefinsand separating the C5 hydrocarbon feedstock into an overheads olefinproduct and a bottoms product. The system may also include an analyzerfor determining a density profile or a composition profile of a diluentcompound within the catalytic distillation reactor system, as well as acontroller configured to adjust one or more operating parameters tomaintain a set point density profile or composition profile of thediluent compound within the catalytic distillation reactor system. Insome embodiments, the analyzer is a density measurement device, and thecontroller may be configured to convert a measured density to anestimated composition. The analyzer may be configured to measure thedensity or composition at an elevation below a feed elevation of themixed hydrocarbon feedstock, and may also be configured to measure thedensity or composition at a sample elevation proximate an elevation ofmaximum rate of change in concentration of the diluent compound withinthe catalytic distillation reactor system.

In another aspect, embodiments disclosed herein relate to a process forproducing C5 olefins from a steam cracker C5 feed, the processincluding: feeding a mixed hydrocarbon stream comprisingcyclopentadiene, linear C5 olefins, cyclic C5 olefins, C5 dienes, andC6+ hydrocarbons to a low temperature/low pressure (LT/LP) distillationcolumn. Concurrently in the LT/LP distillation column, thecyclopentadiene may be reacted to form a dimerized product comprisingdicyclopentadiene, and the mixed hydrocarbon stream may be separated toform a first fraction comprising the C6+ hydrocarbons anddicyclopentadiene and a second fraction comprising the linear and cyclicC5 olefins and C5 dienes. The second fraction and hydrogen may be fed toa catalytic distillation reactor system, wherein the second fraction isintroduced intermediate a first catalyst zone and a second catalystzone. Concurrently in the catalytic distillation reactor system, thelinear C5 olefins may be separated from the cyclic C5 olefins and C5dienes contained in the second fraction, and at least a portion of theC5 dienes may be selectively hydrogenated to form additional C5 olefins.An overhead distillate comprising the linear C5 olefins and a bottomsproduct comprising cyclic C5 olefins may be recovered from the catalyticdistillation reactor system.

The low temperature/low pressure distillation column, in someembodiments, may be operated in liquid continuous distillationoperation. A saturated hydrocarbon diluent stream may also be co-fedwith the second fraction and hydrogen to the catalytic distillationreactor system. The process may further include: purging a portion ofthe bottoms product; reacting a remaining portion of the bottoms productin a total hydrogenation unit to convert the cyclic C5 olefins tocyclopentane; and recycling the cyclopentane to the catalyticdistillation reactor system as the saturated hydrocarbon diluent. Thetotal hydrogenation unit may be operated, for example, at a pressure inthe range from about 220 psia to about 300 psia and at a temperature inthe range from about 200° F. and 260° F. An average residence time inthe low temperature/low pressure distillation column may be in the rangefrom 0.2 hours to 6 hours, such as a residence time is sufficient toallow for greater than 90 wt % of the cyclopentadiene to dimerize. Insome embodiments, the low temperature/low pressure distillation columnmay be operated at a pressure in the range from about 15 psia to about85 psia, at an overhead condenser temperature in the range from about90° F. to about 150° F., and at a reboiler temperature in the range fromabout 155° F. to 300° F.

In another aspect, embodiments disclosed herein relate to a system forproducing C5 olefins from a steam cracker C5 feed. The system mayinclude a low temperature/low pressure distillation column configured toconcurrently (a) fractionate a mixed hydrocarbon stream comprisingcyclopentadiene, linear C5 olefins, cyclic C5 olefins, C5 dienes, andC6+ hydrocarbons to recover an overhead distillate comprising linear andcyclic C5 olefins and C5 dienes, and (b) dimerize the cyclopentadiene.The system may also include a catalytic distillation reactor systemconfigured to concurrently (a) separate the linear C5 olefins from thecyclic C5 olefins and C5 dienes in the overhead distillate and (b)selectively hydrogenate at least a portion of the C5 dienes in theoverhead distillate to form additional C5 olefins. In some embodiments,the system may also include a total hydrogenation unit configured toconvert the cyclic C5 olefins recovered as a bottoms product from thecatalyst distillation reactor system to cyclopentene, as well as ametathesis reactor configured to covert the linear C5 olefins recoveredfrom the catalyst distillate reactor system into propylene.

In another aspect, embodiments disclosed herein relate to a process forproducing olefins including: feeding a mixed hydrocarbon streamcomprising cyclopentadiene, linear C5 olefins, cyclic C5 olefins, C5dienes, and C6+ hydrocarbons to a low temperature/low pressuredistillation column operating in liquid continuous mode. Concurrently inthe low temperature/low pressure distillation column, thecyclopentadiene may be reacted to form a dimerized product comprisingdicyclopentadiene, and the mixed hydrocarbon stream may be fractionatedto form a first fraction comprising the C6+ hydrocarbons anddicyclopentadiene and a second fraction comprising the linear and cyclicC5 olefins and C5 dienes. The process may further include operating thelow temperature/low pressure distillation column at a pressure in therange from about 15 psia to about 85 psia, at an overhead condensertemperature in the range from about 90° F. to about 150° F., and at areboiler temperature in the range from about 155° F. to 300° F. Anaverage residence time in the low temperature/low pressure distillationcolumn may be in the range from 0.2 hours to 6 hours, and the residencetime may be sufficient to allow for greater than 90 wt % of thecyclopentadiene to dimerize.

In yet another aspect, embodiments disclosed herein relate to systemsfor performing the processed described herein. Other aspects andadvantages will be apparent from the following description and theappended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1-5 are simplified flow diagrams of processes to produce C5olefins according to embodiments disclosed herein.

FIGS. 6-7 are simplified flow diagrams of pilot plant setups used toinvestigate processes and catalyst systems to produce C5 olefinsaccording to embodiments disclosed herein.

FIGS. 8-11 are simplified flow diagrams of processes to produce C5olefins according to embodiments disclosed herein.

FIGS. 12 and 13 are schematic diagrams illustrating placement of densitymeasurement devices for processes to produce C5 olefins according toembodiments disclosed herein.

FIGS. 14-16 illustrate simulation results for processes according toembodiments disclosed herein.

FIGS. 17-19 are simplified flow diagrams of pilot plant setups used toinvestigate processes to produce C5 olefins according to embodimentsdisclosed herein.

FIG. 20 is a chart illustrating pilot plant experimental results.

FIG. 21 is a simplified flow diagram of a process to produce C5 olefinsaccording to embodiments disclosed herein.

In the figures, like numerals generally represent like parts.

DETAILED DESCRIPTION

Within the scope of this application, the expression “catalyticdistillation reactor system” denotes an apparatus in which the catalyticreaction and the separation of the products take place at leastpartially simultaneously. The apparatus may comprise a conventionalcatalytic distillation column reactor, where the reaction anddistillation are concurrently taking place at boiling point conditions,or a distillation column combined with at least one side reactor, wherethe side reactor may be operated as a liquid phase reactor or a boilingpoint reactor. While both catalytic distillation reactor systemsdescribed may be preferred over conventional liquid phase reactionfollowed by separations, a catalytic distillation column reactor mayhave the advantages of decreased piece count, reduced capital cost,increased catalyst productivity per pound of catalyst, efficient heatremoval (heat of reaction may be absorbed into the heat of vaporizationof the mixture), and a potential for shifting equilibrium. Divided walldistillation columns, where at least one section of the divided wallcolumn contains a catalytic distillation structure, may also be used,and are considered “catalytic distillation reactor systems” herein.

Feed streams according to embodiments disclosed herein may includevarious refinery streams containing linear and/or iso C5 olefins andvarious dienes and acetylenic compounds. For example, a C4-C6 cut, a C5cut, a C5-C6 cut or other various C5 olefin-containing mixtures may beused. In some embodiments, the feed stream is a C5 fraction containinglinear pentenes, cyclopentene, as well as linear and/or cyclic dieneand/or acetylenic compounds, and may contain C6+ hydrocarbons, such asbenzene and toluene, as well as sulfur containing compounds, such asthiophene, 2-methyl thiophene, 3-methyl thiophene, and isobutylmercaptan, among others. Mixed pentene feedstocks useful in embodimentsdisclosed herein may include linear pentenes and isopentenes. Mixedpentene feedstocks may also include various other hydrocarboncomponents, including C4 to C6 paraffins and olefins. In someembodiments, the mixed pentene feedstock may be a C5 hydrocarbonfraction from a steam cracker, where the C5 fraction may include linearpentenes, isopentene, n-pentanes, isopentanes, as well as cyclopentene,cyclopentadiene, linear and branched C5 dienes, and acetylenes.

The steam cracking process produces C5 hydrocarbon streams that may havea relatively high concentration of cyclopentadiene anddicyclopentadiene, as well as other dienes and acetylenes compared toFCC C5 hydrocarbon streams. For example, FCC C5 streams typicallycontain less than 1 wt % or 2 wt % dienes, whereas steam cracker C5streams may contain 10% or more dienes, such as 15%, 18%, 25%, or 50% ormore dienes. If hydrogenated similar to an FCC C5 product, for example,the additional highly reactive species may result in high rates ofcatalyst fouling and potential runaway reactions. Furthermore, directfeed of the C5 cut to hydrogenation may result in introducing thesulfur-containing compounds present in the C5 cut to the catalyst zone,which could potentially inhibit or damage the catalyst performance.Cyclopentene concentrations must also be controlled in the desired C5olefin product, as cyclopentene may undergo undesirable ring-openingmetathesis polymerization in a downstream metathesis unit, for example.Additionally, hydrogenation of cyclopentadiene may result in additionalcyclopentene formation, which may consume more hydrogen and requiresignificantly higher reflux and reboiler duty to meet overheadcyclopentene specifications.

The above noted problems associated with steam cracker C5 feeds orsimilar feedstocks containing relatively high amounts of highly reactivespecies may be addressed by one or more of the processes disclosedherein. Referring initially to FIG. 1, a simplified flow diagram of aprocess for producing C5 olefins from a mixed hydrocarbon stream 30,such as a steam cracker C5 feed, is illustrated. Mixed hydrocarbonstream 30 may contain cyclopentadiene, linear and branched C5 olefins,linear and branched C5 dienes, cyclic C5 olefins, and C6+ hydrocarbons,among other components as described above.

Mixed hydrocarbon stream 30 may be fed to a selective dimerizationreactor 32, which may be a catalytic or non-catalytic reactor. In someembodiments, dimerization reactor 32 may be a heat soaker. In thedimerization reactor, cyclopentadiene is dimerized to formdicyclopentadiene. Additionally, cyclopentadiene may be reacted withother compounds, such as isoprene, to form heavy olefin compounds.

Following dimerization, effluent 34 may be recovered from dimerizationreactor 32 and fed to a separator 36. Separator 36 may be a distillationcolumn, fractionator, or any other type of separator useful forseparating the dimerization reactor effluent to form a bottoms fraction40 containing the C6+ hydrocarbons, dicyclopentadiene, and other heavycomponents, and an overheads fraction 38 containing the linear,branched, and cyclic C5 olefins, and the linear and branched C5 dienes.Any sulfur compounds contained in the mixed hydrocarbon stream may alsobe recovered with bottoms fraction 40. To obtain the desired separation,separator 36 may be controlled to limit the overhead fraction benzenecontent to less than 0.5 wt %, for example.

The overhead fraction 38 may then be recovered and fed to a catalyticdistillation column reactor 44. Hydrogen 42 and one or more diluentstreams 43, 60 may also be fed to catalytic distillation column reactor44. As illustrated in FIG. 1, catalytic distillation column reactor 44includes a first catalyst zone 46 and a second catalyst zone 47.Overhead fraction 38 is introduced to catalytic distillation columnreactor 44 intermediate first catalyst zone 46 and second catalyst zone47. Hydrogen 42 may be introduced below the lowest catalyst zone,catalyst zone 47 as illustrated, or may be a split feed having hydrogenintroduced below the catalyst zones.

In catalytic distillation reactor system 44, the C5 olefin-containingfeed is concurrently fractionated and selectively hydrogenated. Thelighter components in the C5 olefin-containing feed traverse up thecolumn, where any acetylenes and dienes boiling up into catalyst zone 46may be reacted with hydrogen to produce additional olefins andparaffins, before being recovered as an overheads fraction 48. Theheavier components in the C5 olefin-containing feed traverse down thecolumn into catalyst zone 47, where acetylenes and dienes may be reactedwith hydrogen to produce additional olefins and paraffins. Uponconversion to olefins and paraffins, these lighter boiling componentsmay traverse up the column and be recovered with overheads fraction 48.Heavier boiling components, including unreacted dienes and cyclicolefins, continue to traverse down the column and may be recovered as abottoms fraction 50. The boiling points of various dienes and olefinsare compared in Table 1, illustrating how the selective hydrogenation ofdienes in catalyst zone 47 may result in additional production ofolefins that may be recovered in the overheads.

TABLE 1 C5 normal boiling point comparison. Component Normal BoilingPoint (° F.) Cis-2-pentene 98.5 Trans-2-pentene 97.4 Cyclopentene 111.6Cyclopentane 120.65 Cis-1,3-pentadiene 111.3 1-trans-3-pentadiene 107.6

The inert solvent or diluent stream added via one or both lines 43, 60may contain various saturated hydrocarbons, such as linear, branched orcyclic paraffins, boiling in a similar range as the C5 feedstock.Preferably, the diluent may include or only include higher boilingcomponents, such that the diluent may traverse downward from the feedpoint and be used to dilute the lower portion of column 44, as opposedto the whole of column 44. For example, the inert solvent may includehydrocarbons having a normal boiling point of 102.5° F. or higher, 105°F. or higher, or 107.5° F. or higher, in various embodiments. In thismanner, the diluent may help control the reaction of the dienes andcyclic olefins that may preferentially traverse downward into catalystzone 47. The diluent may also help to wash the catalyst in catalyst zone47, preventing buildup of polymerized byproducts or coke from thecatalyst. In some embodiments, the inert diluent may containcyclopentane, which boils closer to the C5 dienes than to the desired C5olefins in the overhead fraction.

In some embodiments, the diluent stream may be provided by hydrogenatingthe cyclopentene contained in the bottoms fraction 50, as illustrated inFIG. 1. A portion of the bottoms fraction 50 may be purged from thesystem via stream 52, to control buildup of heavies. A remaining portionof the bottoms fraction 50, including cyclopentene and any unreacteddienes, may be fed via stream 54, along with hydrogen 56, tohydrogenation reactor 58. As it is desired to control cyclopentenecontent in the column, hydrogenation reactor 58 may be a totalhydrogenation unit, feeding excess hydrogen to ensure essentiallycomplete conversion of the cyclopentene and dienes in the bottomsfraction. Any unreacted hydrogen may be carried through effluent 60 intocolumn 44, supplying additional hydrogen for the selective hydrogenationprocess occurring within upper reaction zone 46.

Overhead distillate fraction 48 recovered from the catalyticdistillation reactor system 44, and containing the desirable linear andbranched C5 olefins, may then be used in downstream processing. Forexample, the overhead fraction 48 may be fed to a metathesis unit forconverting the linear C5 olefins to propylene.

As mentioned above, it may be desirable to limit the amount ofcyclopentene carried over with the overhead product from column 44.Total hydrogenation unit 58 may convert a significant portion of thecyclopentene, however control of the column may be set to limit overheaddistillate cyclopentene content to less than 0.5 wt %, less than 1.5 wt% or less than 2.5 wt %, for example.

The dimerization reactor 32 may be operated at a pressure in the rangefrom about 100 psia to about 200 psia, such as from about 130 psia toabout 170 psia or from about 140 to about 160 psia, and at a temperaturein the range from about 190° F. to about 270° F., such as from about210° F. to about 250° F. or from about 220° F. to about 240° F. Theresidence time in the dimerization reactor should be sufficient toconvert the cyclopentadiene to dicyclopentadiene, while limiting thethermal reaction of other components, as the dienes may be converted todesirable olefins in column 44, as described above. In some embodiments,the dimerization reaction conditions of temperature, pressure, andresidence time are controlled to achieve at least 90% conversion of thecyclopentadiene, such as at least 92%, at least 93%, at least 93% or atleast 94% cyclopentadiene conversion to heavier compounds, such asdicyclopentadiene.

Separator 36 may be a low temperature/low pressure separator, such as afractionator or distillation column operated at a pressure in the rangefrom about 15 psia to about 85 psia, such as from about 20 psia to about80 psia or from about 25 to about 75 psia, and at a condensertemperature in the range from about 97° F. to about 213° F., such asfrom about 113° F. to 208° F. or from about 126° F. to about 202° F. Asnoted above, separator 36 may be controlled, such as via reflux rate anddistillate to feed ratio, to minimize the amount of sulfurs and benzenein light fraction 38, and to minimize the amount of valuable olefins anddienes (to be converted to olefins downstream) recovered with heaviesfraction 40.

Catalytic distillation reactor system 44 may be operated at a pressurein the range from about 50 psia to about 250 psia, such as from about 60psia to about 240 psia or from about 70 psia to about 230 psia. Toachieve the desired separation and reaction, the system 44 may beoperated with a reboiler temperature in the range from about 220° F. toabout 320° F., and at a hydrogen partial pressure in the range fromabout 1 psi to about 25 psi, such as from about 5 psi to about 20 psi.The reboiler duty and reflux rate required may depend on the overheadspecification on cyclopentene, and the amount of hydrogen required maydepend on the feed concentration of the various dienes, among othervariables.

Total hydrogenation unit 58 may be operated at a pressure in the rangefrom about 220 psia to about 300 psia, such as from about 240 psia toabout 289 psia and at a temperature in the range from about 200° F. and260° F., such as a temperature in the range from about 220° F. to about240° F. To achieve the desired conversion of cyclopentene over ahydrogenation catalyst contained in reactor 58, a hydrogen partialpressure in the range from about 150 psi to about 250 psi may be used,such as a hydrogen partial pressure in the range from about 160 psi toabout 200 psi.

The process as illustrated in FIG. 1 may be used to recover asignificant portion of the olefins contained in the C5 feedstock. Insome embodiments, the process may be operated to achieve a linear olefinrecovery, measured as moles C5 olefins in the overhead distillate 48divided by moles C5 olefins and moles C5 dienes in the mixed hydrocarbonstream 30, of greater than 80%; greater than 82%, greater than 83%,greater than 84%, and greater than 86% in yet other embodiments.

In some embodiments, the process may include a fixed bed selectivehydrogenation reactor 74, as shown in FIG. 2, to convert a portion ofthe dienes in the overhead fraction 38 via reaction with hydrogen 72prior to introducing the overhead fraction 38 into catalyticdistillation reactor system 44. In this manner, the amount of catalystcontained within the distillation column reactor may be reduced orminimized, while achieving the desired selective hydrogenation andseparation. In some embodiments, the selective hydrogenation reactor 74may be in addition to total hydrogenation reactor 58, or may be in lieuof total hydrogenation reactor 58. When used in lieu of totalhydrogenation reactor 58, it should be noted that the concentration ofcyclopentene within the column may be greater than when the cyclopentenerecycle is completely hydrogenated to cyclopentane, and this may affectperformance and control of the catalytic distillation reactor system 44.

In other embodiments, the process may include a feed preheater (notshown) intermediate separator 36 and catalytic distillation reactorsystem 44. The feed preheater may be used to partially vaporize overheadfraction 38 prior to introducing the feed to the catalytic distillationreactor system 44. In this manner, additional dienes may be boiled upinto catalyst zone 46, increasing the residence time of the dienes overcatalyst in zones 46 and 47. Partial vaporization of the feed may resultin additional olefin recovery, or may alternatively be used to reducereboiler duty requirements to achieve a similar olefin recovery ascompared to processes without a feed preheater. For example, the partialvaporizer may be operated at conditions sufficient to vaporize between 5wt % and 95 wt % of the C5 dienes contained in the feed, such as fromabout 10 wt % to about 50 wt % of the dienes in the feed.

It has also been found that additional improvements to olefin recoverymay be made by loosening the specifications on overheads fraction 48.For example, by allowing additional cyclopentene in the overheadfraction, the losses of olefins to the bottoms product, to meet overheadcyclopentene concentration requirements, may be reduced. Additionally,losses of olefins due to excess conversion in catalyst zones 46, 47 dueto increased average residence time (higher reflux ratios, and increasedrecycle of desired olefins through the column), etc., may also bereduced. Overhead fraction 48 may then be fed to a splitter or separator62, as illustrated in FIG. 2, to separate a portion of the cyclopentenefrom the overhead product, resulting in a C5 olefin product stream 66meeting cyclopentene specifications while improving olefin recovery. Thecyclopentene-enriched stream 64 may then be recycled back to totalhydrogenation unit 58, as illustrated, or to selective hydrogenationunit 74 when used in lieu of total hydrogenation unit 58.

In some embodiments, such as illustrated in FIG. 3, catalyticdistillation reactor system 44 may be operated with only a reaction zonelocated above the location at which overhead fraction 38 is introducedto the column. In column 44, the C5 olefin-containing feed isconcurrently fractionated and selectively hydrogenated. The lightercomponents in the C5 olefin-containing feed traverse up the column,where any acetylenes and dienes may be reacted with hydrogen to produceadditional olefins and paraffins, before being recovered as an overheadsfraction 48. The heavier components in the C5 olefin-containing feedtraverse down the column and are recovered as a bottoms fraction 50.

The process of FIG. 3 may incur olefin losses not incurred by theprocess of FIG. 1, due to lack of hydrogenation of dienes that may occurover catalyst zone 47 (FIG. 1). However, as described above, partialvaporization of the feed, such as in a feed preheater 41 (FIG. 3), useof a fixed bed selective hydrogenation unit upstream of column 44, oroperation of column 44 to increase boilup into column 46 coupled withdownstream cyclopentene removal in separator 62, may be used to improveolefin recovery rates, if desired. Use of these alternatives may providea means to achieve a decent olefin recovery while negating the foulingthat may occur in lower catalyst zone 47. The cost/benefit analysis todetermine the best operating system may depend upon the type ofcatalytic distillation reactor system used, the amount, type andreplacement frequency of catalyst in catalyst zone 47, as well as theoverall feed composition.

Low pressure, low temperature separator 36, as described above withrespect to FIG. 1, removes dicyclopentadiene from the mixed hydrocarbonsbeing fed to distillation column reactor system 44. At highertemperatures, such as at temperatures of about 300° F. or greater,dicyclopentadiene may back crack into cyclopentadiene. Introduction ofdicyclopentadiene into catalytic distillation reactor system 44 is thusgenerally not desired, as the dicyclopentadiene may be exposed torelatively high temperatures in the column reboiler, back crack to formcyclopentadiene, which although it may be subsequently hydrogenated tocyclopentene in column 44, the additional cyclic olefins and dienesbeing pushed up the column may result in a need for increased refluxrates to meet overhead specifications. The use of low temperature, lowpressure separator 36 avoids this scenario.

It has been found that dicyclopentadiene back cracking may also beavoided via limiting the reboiler temperature and residence time/holdupin the reboiler of column 44. For example, as illustrated in FIG. 4, thedimerization reactor 32 effluent 34 may be fed into a catalyticdistillation reactor system 80, which may have one or more reactionzones 86. In column 80, the C5 olefin-containing feed is concurrentlyfractionated and selectively hydrogenated with hydrogen fed via flowline 82. The lighter components in the C5 olefin-containing feedtraverse up the column, where any acetylenes and dienes may be reactedwith hydrogen to produce additional olefins and paraffins, before beingrecovered as an overheads fraction 88. The heavier components in the C5olefin-containing feed, including the dicyclopentadiene and C6+components in the feed, traverse down the column and are recovered as abottoms fraction 90.

A portion of bottoms fraction 90 may be reboiled and fed back to thecolumn, such as via reboiler 91. The remaining portion of the bottomsfraction may be recovered as a bottoms product 92. As described forFIGS. 1-3, a feed preheater may be used to increase boilup of dienesinto catalyst zone 86; one benefit of the feed preheater noted above wasdecreased reboiler duty. Additionally or as an alternative, the columnmay include an intermediate reboiler 99. A side draw may be withdrawnfrom column 80 below the feed location for hydrogen 82 and feed 34, andabove main reboiler 91. The side draw may be at least partiallyvaporized in intermediate reboiler 99, and returned to column 80. Thenumber of intermediate reboilers and temperatures of same should besufficient to provide the desired vapor traffic in the column whilelimiting the temperature of the intermediate and main reboilers, such asto a temperature of less than about 300° F., and also reducing orminimizing the liquid holdup in the main reboiler. In this manner, thedesired column traffic may be maintained while limiting the amount ofback cracking occurring in the main reboiler.

As a drawback, activity of the hydrogenation catalyst is typicallyreduced as column temperature is reduced. The intermediate reboilers mayprovide a means to maintain catalyst activity while limiting the backcracking of dicyclopentadiene. Additionally, such a configuration mayprovide for reduced capital and operating requirements, eliminating oneor more pieces of equipment, including the low temperature, low pressureseparator. The total reboiler duty (intermediate plus main) has alsobeen found to be roughly the same to meet cyclopentene specifications inthe overhead product.

Catalysts useful in the hydrogenation reaction zone(s) may include Group8 metals, such as cobalt, nickel, palladium, or platinum, alone or incombination, and/or Group 1B metals, such as copper, and/or othermetals, such as a Group 5A or Group 6A metals, such as molybdenum ortungsten, on a suitable support, such as alumina, silica, titania,silica-alumina, titania-alumina, titania-zirconia, or the like. Normallythe catalytic metals are provided as the oxides of the metals supportedon extrudates or spheres. The metals may be reduced to the hydride formor other active states, if necessary, prior to use by exposure tohydrogen, for example.

The particular catalyst(s) and operating conditions in the hydrogenationreaction zone(s) may depend upon the particular C5-olefing containingfeed(s) used, the overall flow scheme (i.e., use of or lack of guardbeds, etc.), the desired conversion and selectivity, and the tolerancein end products for any isomerization that may occur under hydrogenationconditions, among other variables. Typical hydrogenation reaction zoneoperating conditions include temperatures in the range from 30° C. to500° C. and pressures ranging from 1 to 100 bar.

Objectives of the overall system may include conversion of dienes toolefins, reducing the diene content to less than 500 ppmw, such as lessthan 200 ppmw, for example, as well as to minimize the loss ofunsaturates, i.e., conversion of olefins to paraffins. When combinedwith a downstream metathesis process, linear olefin recovery may beconsidered more important than iso-olefin recovery because, in adownstream methathesis unit, one mole linear C5 olefin can theoreticallyproduce three moles of propylene, while one mole of branched C5 olefincan produce one mole of propylene.

In addition to control of catalytic distillation reactor systemoperating parameters, it has been found that the catalyst used in eachrespective reaction zone may have an impact on overall systemperformance in meeting the objectives of reducing diene content andmaximizing olefin recovery. In particular, it has been found that acatalyst system using a combination of palladium and nickel catalystsmay provide sufficient activity and selectivity to meet the objective ofreducing diene content at a very high olefin recovery.

In some embodiments, the catalyst system is divided into three reactionzones. A first reaction zone, located below the mixed C5 hydrocarbonfeed point, contains a nickel-based catalyst. A second reaction zone,located above the mixed C5 hydrocarbon feed point, also contains anickel-based catalyst. A third reaction zone is disposed above thesecond reaction zone and contains a palladium-based catalyst.

In addition to meeting the above objectives, the palladium and nickelcatalyst systems described herein have been found to be extremelyrobust, maintaining activity and selectivity over extended run lengths.As would be appreciated by one skilled in the art, the expense anddowntime associated with replacing catalysts in a catalytic distillationreactor system are different than those for fixed bed reactors, and thusthe robustness of the catalyst systems herein is a significant benefit.

Referring now to FIG. 5, a catalytic distillation reactor system forproducing C5 olefins and including a catalyst system according toembodiments herein is illustrated. A C5-olefin containing stream 10,such as described above and containing linear pentenes, dienes,acetylenes, cyclopentane, and cyclopentene, and a hydrogen stream 12 maybe fed to a catalytic distillation reactor system 14.

Catalytic distillation reactor system 14 may include two or morereaction zones above the C5 feed elevation, and/or one or more reactionzones below the C5 feed elevation. The reaction zones disposed below thefeed elevation contain a nickel-based catalyst. One or more lowermostreaction zones disposed above the feed elevation also contain anickel-based catalyst. One or more uppermost reaction zones disposedabove the feed elevation contain a palladium-based catalyst.

As illustrated, catalytic distillation reactor system 14 includes tworeaction zones 16, 17 disposed above the C5 feed elevation and onereaction zone 18 disposed below the C5 feed elevation. Reaction zones 17and 18 contain a nickel based catalyst, and Reaction zone 16 contains apalladium based catalyst. Hydrogen 12 may be introduced to the columnbelow the lowermost reaction zone, zone 18, or may be split fed belowtwo or more of the reaction zones.

In catalytic distillation reactor system 14, acetylenes and dienes inthe C5 feed are selectively hydrogenated over the nickel-based andpalladium-based hydrogenation catalyst, converting the acetylenes anddienes to olefins. Concurrent with the selective hydrogenation, the C5feed is fractionated into an overheads fraction 20, including theolefins, and a bottoms fraction 22, including heavier or higher boilingfeed components, such as unreacted dienes as well as cyclopentene andcyclopentane.

A portion of the bottoms fraction 22 may be vaporized in reboiler 23 andreturned to column 14, and a remaining portion of the bottoms fraction22 may be recovered as a bottoms product 24. The overhead fraction 20may be condensed, a portion of the condensed overheads being returned tocolumn 14 as a reflux, and a remaining portion being recovered as anoverhead product fraction 25.

The nickel-based catalyst may include from about 1 wt % to about 40 wt %nickel, or from about 2 wt % to about 60 wt % nickel oxide, on asupport. For example, useful nickel-based catalysts may have from about3 wt % to about 40 wt % nickel, such as from about 5 wt %, 7.5 wt %, 10wt % or 12.5 wt % to about 17.5 wt %, 20 wt %, 22.5 wt % or 25 wt %nickel, where any lower limit may be combined with any upper limit. Thenickel may be disposed on any suitable support, such as silica, titania,alumina, clays, or diatomaceous earth, among others. The catalysts, insome embodiments, may be formed as an extrudate, such as in the form ofpellets or spheres having a nominal size in the range from about 0.25 toabout 5 mm, such as from about 0.5 to about 2.5 mm. The nickel-basedcatalysts may have a BET surface area in the range from about 20 toabout 400 m²/g, such as from about 40 to about 300 m²/g in someembodiments and from about 60 to about 240 m²/g in yet otherembodiments, and may have a pore volume in the range from about 0.1 toabout 0.8 ml/g, such as from about 0.2 ml/g to about 0.7 ml/g in someembodiments, and from about 0.25 to about 0.65 ml/g in yet otherembodiments.

The palladium-based catalyst may include from about 0.1 wt % to about 3wt % palladium, and the catalyst may be supplied in oxide form. Forexample, useful palladium-based catalysts may have from about 0.1 wt %to about 2.5 wt % palladium, such as from about 0.15 wt %, 0.2 wt %,0.25 wt % or 0.3 wt % to about 0.6 wt %, 0.7 wt %, 0.8 wt % or 1.0 wt %palladium, where any lower limit may be combined with any upper limit.The palladium may be disposed on any suitable support, such as silica,titania, alumina, clays, or diatomaceous earth, among others. Thecatalysts, in some embodiments, may be formed as an extrudate, such asin the form of pellets or spheres having a nominal size in the rangefrom about 0.25 to about 5 mm, such as from about 1.0 to about 4.0 mm.The palladium-based catalysts may have a BET surface area in the rangefrom about 20 to about 600 m²/g, and may have a pore volume in the rangefrom about 0.1 to about 1.0 ml/g, in various embodiments.

The above-described catalyst systems, including nickel-based andpalladium-based catalysts, have been found useful in achieving a highdiene conversion rate and a high olefin recovery rate. For example,diene conversion rates may be greater than 98 wt % in some embodiments;greater than 99 wt % in other embodiments, and greater than 99.5 wt % inyet other embodiments. Linear unsaturated recovery, defined as moleslinear C5 olefins in the overhead distillate divided by moles linear C5olefins and dienes in the mixed hydrocarbon stream, may be greater than90% in some embodiments; greater than 92.5 wt % in other embodiments;greater than 95 wt % in other embodiments; and greater than 97.5 wt % inyet other embodiments. Branched unsaturated recoveries of greater than90%, 91% or 92% are also possible.

Many of the references noted above indicate that nickel-based catalystshave poor selectivity as well as short catalyst life. However, inaddition to the high selectivity noted above, the above-describedcatalyst system useful in embodiments herein have been found to be verystable, with experiments performed having exhibited no significantlosses to activity or selectivity during over more than a year ofoperations. Overall, the unique combination and configuration of thecatalytic distillation reactor systems and the catalyst systemsdescribed herein used therein may provide superior C5 olefin selectivityand catalyst stability.

With regard to the nickel-based catalysts, many of the references notedabove suggest that a sulfiding step is required to achieve the desiredactivity and selectivity. In contrast, it has been found that asulfiding step is not necessary, and processes according to embodimentsherein may be performed without sulfiding the nickel-based catalystswhile achieving very high diene conversion and olefin recovery rates.

In some embodiments, hydrogenation reaction zone temperatures may bewithin the range from about 30° C. to about 300° C. In otherembodiments, hydrogenation reaction zone temperatures may be within therange from about 40° C. to about 250° C.; from about 50° C. to about200° C. in other embodiments; and in the range from about 75° C. toabout 175° C. in yet other embodiments. In embodiments where an upperand lower reaction zone are provided, the temperature in the lower bedwill be greater than that of the upper bed, both of which are generallycaptured by the above ranges. Overheads and bottoms temperatures of thecolumn may be greater than or less than the temperatures indicatedabove, the bottoms operating at a temperature proximate the boilingrange of the heavier feed components at column pressure, and theoverheads operating at a temperature proximate the boiling range of thelighter feed components and reaction products at column pressure.

Following selective hydrogenation of the acetylenic and diene compoundsand separation of the linear and branched pentenes from cyclopentene,the resulting C5 olefin-containing product may be fed to a metathesisreactor for the production of propylene. For example, the linearpentenes may be reacted with ethylene in the presence of a metathesiscatalyst or a combined metathesis/isomerization catalyst to producepropylene. When linear pentenes are fed to a conventional metathesisreactor, the following reactions may occur:1-pentene-→2-pentene(Isomerization);  (a)2-pentene+ethylene-→1-butene+propylene(Metathesis);  (b)1-butene-→2-butene(Isomerization);  (c)2-butene+ethylene-→2 propylene(Metathesis).  (d)1-Pentene is isomerized to 2-pentene. The metathesis reaction of1-pentene with ethylene is non-productive (products are same asreactants). The overall linear C5 olefin reaction can thus be shown as:1 linear pentene+2 ethylene-→3 propylene.Thus, the primary olefin of interest where metathesis is performeddownstream is the linear pentenes. Branched pentenes provide 1 mole ofpropylene per mole.

The metathesis reaction products, including unreacted ethylene,propylene, butenes, and unreacted pentenes may then be recovered andforwarded to a separation zone, which may include one or moredistillation columns and/or extractive distillation columns forseparating the metathesis reactor effluent into various desiredfractions, which may include an ethylene fraction, a propylene fraction,a butene and/or pentene fraction, and a heavies fraction. The ethylenefraction and butene/pentene fraction(s) may be recycled to themetathesis reaction zone for continued production of propylene.

Catalysts useful in the metathesis reactor may include any knownmetathesis catalyst, including oxides of Group VIA and Group VIIA metalson supports. Catalyst supports can be of any type and could includealumina, silica, mixtures thereof, zirconia, and zeolites. In additionto the metathesis catalyst, the catalyst contained in the metathesisreactor may include a double bond isomerization catalyst such asmagnesium oxide or calcium oxide, for converting 1-butene and 1-penteneto 2-butene and 2-pentene, allowing for increased production ofpropylene via metathesis with ethylene. In some embodiments, thecatalyst may include a promoter to reduce acidity; for example, analkali metal (sodium, potassium or lithium), cesium, a rare earth, etc.In some embodiments, the metathesis or mixed metathesis/double bondisomerization catalyst may include those described in US20110021858 orUS20100056839, for example.

The metathesis reactor may operate at a pressure between 1 and 40 bar insome embodiments, and between 5 and 15 bar in other embodiments. Themetathesis reactor may be operated such that the reaction temperature iswithin the range from about 50° C. to about 600° C.; within the rangefrom about 200° C. to about 450° C. in other embodiments; and from about250° C. to about 400° C. in yet other embodiments. The metathesisreaction may be performed at a weight hourly space velocity (WHSV) inthe range from about 3 to about 200 in some embodiments, and from about6 to about 40 in other embodiments. The reaction may be carried out inthe liquid phase or the gas phase, depending on structure and molecularweight of the olefin(s), by contacting the olefin(s) with the metathesiscatalyst. If the reaction is carried out in the liquid phase, solventsor diluents for the reaction can be used, such as aliphatic saturatedhydrocarbons, e.g., pentanes, hexanes, cyclohexanes, dodecanes, andaromatic hydrocarbons such as benzene and toluene are suitable. If thereaction is carried out in the gaseous phase, diluents such as saturatedaliphatic hydrocarbons, for example, methane, ethane, and/orsubstantially inert gases, such as nitrogen and argon, may be present.For high product yield, the reaction may be conducted in the absence ofsignificant amounts of deactivating materials such as water and oxygen.

Examples 1-3

Simulations were conducted to compare the performance of systems forselectively hydrogenating a C5 feed stream according to variousembodiments herein. Simulations were carried out in ASPEN PLUS 7.2(Aspen Technology, Inc., Burlington, Mass.).

Example 1

In this Example, a process similar to that as illustrated in FIG. 1 issimulated. In the simulations, dienes and acetylenes are assumed to beselectively hydrogenated into olefins in the catalytic distillationreactor system, and all olefins are assumed to be saturated into alkanesin the total hydrogenation unit. Process conditions were as follows:

TABLE 2 Process Conditions for Example 1 Example # 1 Heat soaker (32)Pressure, psia 150 Temperature, ° F. 230 CPD conversion   94% Low P/Tcolumn (36) Pressure, psia 29.7 Column stages 30 Condenser temp, ° F.136.7 Reboiler temp, ° F. 246.6 Feed stage 14 Thiophene in distillate,ppm 0 Benzene in distillate, wt % 0.5 wt % C5 olefin recovery, %   100%C5CDHYDRO column (44) Column stages 102 C5 feed stage 42 H2 feed stage60 Reaction zone stages 30-40 43-50 Cyclopentene in OVHD, wt %  0.5%Linear olefin recovery, % 84.79% Total olefin recovery, % 82.07%Pressure, psia 135 Mass reflux ratio 11.94 Reboiler duty, btu/hr 1.37e+7Bottom vs. feed molar ratio 0.555 PPH2, psi 15.2 Total HydrogenationUnit (58) Pressure, psia 260 Temperature, ° F. 230 PPH2, psi 181 Recyclevs. feed molar ratio 1.23

The simulated mass balance for Example 1 is shown in Table 3.

TABLE 3 Stream Vent Mass Flow lb/hr 30 34 38 40 54 60 48 52 Loss C4s46.29 46.29 46.29 0.00 0.00 0.00 26.70 0.00 19.58 N-PENTANE 576.77576.77 576.76 0.01 31.95 187.93 660.40 7.50 64.85 2-METHYL- 641.04641.04 641.04 0.00 0.00 229.21 754.06 0.00 116.19 BUTANE CYCLO 89.6489.64 83.74 5.91 4021.15 4881.17 0.55 943.23 0.03 PENTANE CYCLO 651.19651.19 645.16 6.02 835.30 0.00 26.02 195.94 1.93 PENTENE CYCLO 6718.23403.09 401.76 1.33 0.00 0.00 0.00 0.00 0.00 PENTADIENE DICYCLO 0.005844.86 0.00 5844.86 0.00 0.00 0.00 0.00 0.00 PENTADIENE 1-PENTENE719.41 719.41 719.40 0.01 0.02 0.00 633.63 0.00 85.75 CIS-2-PENTENE118.40 118.40 118.38 0.02 76.62 0.00 573.88 17.97 53.88 TRANS-2- 193.38193.38 193.35 0.03 74.98 0.00 1306.09 17.59 125.32 PENTENE 2-METHYL-448.22 448.22 448.21 0.01 0.04 0.00 396.34 0.01 51.82 1-BUTENE 2-METHYL-0.00 0.00 0.00 0.00 222.76 0.00 1029.58 52.25 84.50 2-BUTENE 3-METHYL-60.89 60.89 60.89 0.00 0.00 0.00 49.66 0.00 11.23 1-BUTENE 2-METHYL-1834.04 1349.42 1349.16 0.26 0.00 0.00 0.00 0.00 0.00 1,3-BUTADIENECIS-1,3- 591.99 591.99 586.62 5.37 0.00 0.00 0.00 0.00 0.00 PENTADIENE1-TRANS- 940.42 940.42 935.61 4.81 0.00 0.00 0.00 0.00 0.00 3-PENTADIENE1,4-PENTADIENE 347.86 347.86 347.86 0.00 0.00 0.00 0.00 0.00 0.001,2-PENTADIENE 9.02 9.02 8.91 0.11 0.00 0.00 0.00 0.00 0.00 BENZENE19148.88 19148.88 39.51 19109.37 32.00 0.00 0.00 7.51 0.00 C6+ 22864.3223819.21 697.91 23121.31 3168.05 3213.22 0.00 743.12 0.00 HYDROGEN 0.000.00 0.00 0.00 0.00 51.34 1.00 0.00 442.53 Total flow 55999.99 55999.997900.56 48099.43 8462.88 8562.88 5457.90 1985.12 1057.61

Example 2

In this Example, a process similar to that as illustrated in FIGS. 2 and3 is simulated (Example 2A=no feed preheater; Example 2B=with feedpreheater; Example 2C=with cyclopentene removal column). In thesesimulations, dienes and acetylenes are assumed to be selectivelyhydrogenated into olefins in the catalytic distillation reactor system,and all olefins are assumed to be saturated into alkanes in the totalhydrogenation unit. Process conditions were as follows:

TABLE 4 Simulation conditions for Examples 2A, 2B, and 2C Case# 2A 2B 2CHeat soaker (32) Pressure, psia 150 150 150 Temperature, ° F. 230 230230 CPD conversion   94%   94%   94% Low P/T column (36) Pressure, psia29.7 29.7 29.7 Column stages 30 30 30 Condenser temp, ° F. 136.7 136.7136.7 Reboiler temp, ° F. 246.6 246.6 246.6 Feed stage 14 14 14Thiophene in distillate, ppm 0 0 0 Benzene in distillate, wt % 0.5 wt %0.5 wt % 0.5 wt % C5 olefin recovery, %   100%   100%   100% Feed Heater(41) Heat Duty, btu/h 0 1.22e+6 (35% vapor fraction) C5CDHYDRO column(44) Column stages 102 102 52 C5 feed stage 42 42 22 H2 feed stage 60 6040 Reaction zone 30-40 30-40 10-20 Cyclopentene in OVHD, wt %  0.5% 0.5%  11.8% Linear olefin recovery, % 74.63% 75.74% 82.40% Total olefinrecovery, % 81.02% 81.09% 84.15% Pressure, psia 135 135 135 Mass refluxratio 17.72 14.16 6.08 Reboiler duty, btu/hr 2.32e+7 1.70e+7 7.21e+6Bottom vs. feed molar ratio 0.569 0.570 PPH2, psi 10.5 12.9 12.9 TotalHydrogenation Unit (58) Pressure, psia 260 260 260 Temperature, ° F. 230230 230 PPH2, psi 181 181 179 Recycle vs. feed molar ratio 1.18 1.17 1.0Cyclopentene Removal Column (62) Column stages 65 Feed stage 40Cyclopentene in OVHD, wt %  0.5% Reboiler duty, btu/hr 1.48e+7 Pressure,psia 74.7

The simulated mass balance for Examples 2A, 2B, and 2C are shown inTables 5, 6, and 7, respectively.

TABLE 5 Example 2A Stream Vent Mass Flow lb/hr 30 34 38 40 54 60 48 52Loss C4s 46.29 46.29 46.29 0.00 0.00 0.00 26.64 0.00 19.65 N-PENTANE576.77 576.77 576.76 0.01 0.14 428.65 914.79 0.03 90.46 2-METHYL- 641.04641.04 641.04 0.00 0.00 1.31 556.10 0.00 86.25 BUTANE CYCLO 89.64 89.6483.74 5.91 4021.80 4881.69 0.28 943.38 0.02 PENTANE CYCLO 651.19 651.19645.16 6.02 831.41 0.00 26.14 195.02 1.95 PENTENE CYCLO 6718.23 403.09401.76 1.33 3.65 0.00 0.00 0.86 0.00 PENTADIENE DICYCLO 0.00 5844.860.00 5844.86 0.00 0.00 0.00 0.00 0.00 PENTADIENE 1-PENTENE 719.41 719.41719.40 0.01 0.00 0.00 633.12 0.00 86.28 CIS-2-PENTENE 118.40 118.40118.38 0.02 0.34 0.00 464.96 0.08 43.98 TRANS- 193.38 193.38 193.35 0.030.29 0.00 1115.31 0.07 107.82 2-PENTENE 2-METHYL- 448.22 448.22 448.210.01 0.00 0.00 396.07 0.00 52.14 1-BUTENE 2-METHYL- 0.00 0.00 0.00 0.001.09 0.00 1281.56 0.25 105.95 2-BUTENE 3-METHYL- 60.89 60.89 60.89 0.000.00 0.00 49.60 0.00 11.29 1-BUTENE 2-METHYL- 1834.04 1349.42 1349.160.26 0.18 0.00 0.01 0.04 0.00 1,3-BUTADIENE CIS-1,3- 591.99 591.99586.62 5.37 167.56 0.00 0.00 39.31 0.00 PENTADIENE 1-TRANS-3- 940.42940.42 935.61 4.81 233.74 0.00 0.00 54.83 0.00 PENTADIENE 1,4-PENTADIENE347.86 347.86 347.86 0.00 0.00 0.00 0.02 0.00 0.00 1,2-PENTADIENE 9.029.02 8.91 0.11 2.64 0.00 0.00 0.62 0.00 BENZENE 19148.88 19148.88 39.5119109.37 32.00 0.00 0.00 7.51 0.00 C6+ 22864.32 23819.21 697.91 23121.313168.02 3213.22 0.00 743.12 0.00 HYDROGEN 0.00 0.00 0.00 0.00 0.00 38.011.00 0.00 444.12 Total flow 56000.0 56000.0 7900.6 48099.4 8462.9 8562.95465.6 1985.1 1049.9

TABLE 6 Example 2B Stream Vent Mass Flow lb/hr 30 34 38 40 54 60 48 52Loss C4s 46.29 46.29 46.29 0.00 0.00 0.00 26.64 0.00 19.64 N-PENTANE576.77 576.77 576.76 0.01 3.37 401.96 886.89 0.79 87.65 2-METHYL- 641.04641.04 641.04 0.00 0.00 27.91 579.18 0.00 89.78 BUTANE CYCLO 89.64 89.6483.74 5.91 4021.01 4880.92 0.47 943.20 0.03 PENTANE CYCLO 651.19 651.19645.16 6.02 820.41 0.00 26.13 192.44 1.95 PENTENE CYCLO 6718.23 403.09401.76 1.33 14.35 0.00 0.00 3.37 0.00 PENTADIENE DICYCLO 0.00 5844.860.00 5844.86 0.00 0.00 0.00 0.00 0.00 PENTADIENE 1-PENTENE 719.41 719.41719.40 0.01 0.00 0.00 633.16 0.00 86.24 CIS-2-PENTENE 118.40 118.40118.38 0.02 6.46 0.00 480.61 1.51 45.43 TRANS-2- 193.38 193.38 193.350.03 5.63 0.00 1132.54 1.32 109.42 PENTENE 2-METHYL- 448.22 448.22448.21 0.01 0.00 0.00 396.09 0.00 52.12 1-BUTENE 2-METHYL- 0.00 0.000.00 0.00 24.40 0.00 1252.13 5.72 103.46 2-BUTENE 3-METHYL- 60.89 60.8960.89 0.00 0.00 0.00 49.61 0.00 11.28 1-BUTENE 2-METHYL- 1834.04 1349.421349.16 0.26 2.66 0.00 0.00 0.62 0.00 1,3-BUTADIENE CIS-1,3- 591.99591.99 586.62 5.37 148.17 0.00 0.00 34.76 0.00 PENTADIENE 1-TRANS-3-940.42 940.42 935.61 4.81 214.08 0.00 0.00 50.22 0.00 PENTADIENE1,4-PENTADIENE 347.86 347.86 347.86 0.00 0.00 0.00 0.00 0.00 0.001,2-PENTADIENE 9.02 9.02 8.91 0.11 2.32 0.00 0.00 0.54 0.00 BENZENE19148.88 19148.88 39.51 19109.37 32.00 0.00 0.00 7.51 0.00 C6+ 22864.3223819.21 697.91 23121.31 3168.03 3213.22 0.00 743.12 0.00 HYDROGEN 0.000.00 0.00 0.00 0.00 38.87 1.00 0.00 444.03 Total flow 56000.0 56000.07900.6 48099.4 8462.9 8562.9 5464.5 1985.1 1051.0

TABLE 7 Example 2C Stream Mass Flow lb/hr 30 34 38 40 54 60 48 52 66 64C4s 46.29 46.29 46.29 0.00 0.00 0.00 46.29 0.00 46.29 0.00 N-PENTANE576.77 576.77 576.76 0.01 11.84 272.33 847.80 1.35 834.55 13.252-METHYL- 641.04 641.04 641.04 0.00 0.03 103.99 745.01 0.01 744.98 0.03BUTANE CYCLO 89.64 89.64 83.74 5.91 4043.13 4901.37 936.25 4048.89 0.06936.19 PENTANE CYCLO 651.19 651.19 645.16 6.03 825.41 0.00 832.29 216.8131.40 800.89 PENTENE CYCLO 6718.23 403.09 401.76 1.33 7.93 0.00 0.009.77 0.00 0.00 PENTADIENE DICYCLO 0.00 5844.86 0.00 5844.86 0.00 0.000.00 0.00 0.00 0.00 PENTADIENE 1-PENTENE 719.41 719.41 719.40 0.01 0.130.00 719.36 0.04 719.24 0.12 CIS-2- 118.40 118.40 118.38 0.02 19.99 0.00610.79 1.21 587.35 23.44 PENTENE TRANS-2- 193.38 193.38 193.35 0.0326.40 0.00 1377.76 1.72 1346.94 30.82 PENTENE 2-METHYL- 448.22 448.22448.21 0.01 0.15 0.00 448.17 0.05 448.03 0.14 1-BUTENE 2-METHYL- 0.000.00 0.00 0.00 97.30 0.00 1382.80 1.85 1264.67 118.12 2-BUTENE 3-METHYL-60.89 60.89 60.89 0.00 0.00 0.00 60.89 0.00 60.89 0.00 1-BUTENE2-METHYL- 1834.04 1349.42 1349.16 0.26 3.50 0.00 0.00 4.32 0.00 0.001,3- BUTADIENE CIS-1,3- 591.99 591.99 586.62 5.37 86.93 0.00 0.00 107.180.00 0.00 PENTADIENE 1-TRANS-3- 940.42 940.42 935.61 4.81 112.34 0.000.00 138.51 0.00 0.00 PENTADIENE 1,4- 347.86 347.86 347.86 0.00 0.050.00 0.00 0.06 0.00 0.00 PENTADIENE 1,2- 9.02 9.02 8.91 0.11 1.44 0.000.00 1.77 0.00 0.00 PENTADIENE BENZENE 19148.88 19148.88 39.51 19109.3732.05 0.00 0.00 39.51 0.00 0.00 C6+ 22864.32 23819.21 698.94 23120.283194.30 3239.57 11.55 3926.94 0.00 11.55 HYDROGEN 0.00 0.00 0.00 0.000.00 45.64 195.59 0.00 195.59 0.00 Total flow 55999.99 55999.99 7901.5948098.41 8462.90 8562.90 8214.55 8500.00 6280.00 1934.56

Comparing Example 1 to Example 2A, it can be seen from Tables 2 and 4that a much lower reflux ratio/reboiler duty is required when addingsome catalysts below the feed point in Example 1. The required catalyticdistillation reactor system reboiler duty is 2.32e+7 btu/hr for Example2A, while the required reboiler duty is 1.37e+7 btu/hr for Example 1.Without being bound to any particular theory, this may be due to thefact that the linear C5 dienes (e.g., cis-1,3-pentadiene and1-trans-3-pentadiene) are heavier than linear C5 olefins. Hence someportion of dienes will move down toward the reboiler and get purged outfrom the column bottom stream for Example 2A. In Example 2A, the loss ofcis-1,3-pentadiene and 1-trans-3-pentadiene to the bottom stream is206.87 lb/hr and 288.57 lb/hr respectively, while in Example 1, the lossof cis-1,3-pentadiene and 1-trans-3-pentadiene is 0 lb/hr (simulationassumed complete conversion), as shown in Tables 3 and 5.

Comparing Examples 2A and 2C with respect to use of a cyclopenteneremoval column, it can be seen from Table 2 that a much shorter columnand lower reflux ratio/reboiler duty are required for the catalyticdistillation reactor system. The required column reboiler duty is2.32e+7 btu/hr for Example 2A, while the required reboiler duty is7.21e+6 btu/hr for Example 2C. In Example 2A the loss ofcis-1,3-pentadiene and 1-trans-3-pentadiene to the bottom stream is206.87 lb/hr and 288.57 lb/hr respectively, while in Example 2C, theloss of cis-1,3-pentadiene and 1-trans-3-pentadiene is 107.18 lb/hr and138.51 lb/hr (Please see Table 5 and Table 7).

Comparing Examples 2A and 2B with respect to use of a feed preheater, itcan be seen from Example 2A that the process can be successfully used totreat the stream cracker C5 feed to meet the downstream metathesis unit.Advantageously, the present inventors have discovered that adding asmall preheater into the feed stream (Example 2B) may result in asubstantial reduction in the reflux ratio or reboiler duty of thecatalytic distillation reactor system. The required column reboiler dutyis 2.32e+7 btu/hr for Example 2A without a pre feed heater, while therequired reboiler duty is 1.70e+7 btu/hr for Example 2B with a small prefeed heater (1.22e+6 btu/hr). Without being bound to any particulartheory, this may be due to the fact that the linear C5 dienes (e.g.,cis-1,3-pentadiene and 1-trans-3-pentadiene) are heavier than linear C5olefins. Hence some portion of dienes will move down toward the reboilerand are contained in the bottoms stream. In Example 2A the loss ofcis-1,3-pentadiene and 1-trans-3-pentadiene to the bottom stream is206.87 lb/hr and 288.57 lb/hr respectively, while in Example 2B, theloss of cis-1,3-pentadiene and 1-trans-3-pentadiene is 182.93 lb/hr and264.3 lb/hr respectively (Please see Table 5 and Table 6). Bypre-vaporizing C5 diene feed, more C5 dienes will move up into thereaction zone and get hydrogenated into valuable linear C5 olefins.Therefore, at a similar linear C5 olefin recovery rate, the columnreflux ratio/reboiler duty could be substantially reduced by adding apre-heater to pre-vaporize the C5 diene feed.

Example 3

Steam cracker C5 dienes selective hydrogenation over palladium catalyst(about 0.6 wt % palladium on an alumina support) and nickel-basedcatalyst (33.3 wt % nickel on a support) were studied in a pilot plant.The objective of the pilot plant experiments was to reduce dienes fromvery high levels down to a very low level while minimizing the loss ofunsaturates. In particular linear olefin recovery was considered moreimportant than iso-olefin recovery; in a downstream methathesis unit,one mole linear C5 olefin can theoretically produce three moles ofpropylene, while one mole of branched C5 olefin can produce one mole ofpropylene. A simplified flow diagram of the pilot plant configurationused is illustrated in FIGS. 6 and 7, similar to the overall embodimentof FIG. 1.

Referring now to FIG. 6, C5 feed purification was performed by feeding apygas 100 and a cyclopentane stream 102 to a distillation column 104.Column 104 was entirely filled with Raschig super rings. The aromaticsand C6+ hydrocarbons were separated as bottom product 106 while the C5hydrocarbons were recovered in the overhead stream 108. The overheadproduct stream was then used as a feed to the catalytic distillationreactor systems described below with respect to FIG. 7.

The catalytic distillation reactor systems 200 of FIG. 7, includes adistillation column reactor system 200 split into a stripping section201 and a rectifying section 202. The stripping section 201 (below theelevation of feed 108 introduction) includes one reaction zone 204containing a selective hydrogenation catalyst, and the rectifyingsection (above the elevation of feed 108 introduction) includes tworeaction zones 206, 208 containing a selective hydrogenation catalyst.Reaction zones 204 and 206 contain the nickel-based catalyst, andreaction zone 208 contains the palladium-based catalyst. Hydrogen 210,212 is introduced below reaction zones 204, 206, respectively. Dienes infeed 108 are converted within column 200 to olefins and recovered in thedistillate product 216. The catalyst zones 206, 208 above the feed wereused to convert light dienes such as isoprene and cyclopentadiene.Heavier linear dienes traverse down and were reacted in catalyst zone204 to prevent significant yield loss to the bottoms product 218.Rectifying section 202 was charged with 8 ft of Raschig super rings atthe top followed by 14 ft of palladium catalyst and 7 ft of nickelcatalyst. Stripper section 201 was filled with 6 ft of Raschig superrings at the top followed by 7 ft of nickel catalyst and 18 ft ofRaschig super rings.

Test conditions for and results from the pilot plant experiments areexemplified by the selection of data presented in Table 8-13 below.

TABLE 8 Column 104 Conditions. Sample Time Condition 1 2 3 4 Pressure(psig) 40 40 40 40 Reboiler Temp (° F.) 310.9 310.8 311.6 310.6Condenser Temp (° F.) 83.9 85.4 88 83.8 Mixed C5 Feed Rate (lb/h) 60 6060 60 Cyclopentane Feed Rate (lb/h) 10 10 10 10 Overhead Draw Rate(lb/h) 17.9 18 18 18

TABLE 9 Column 200 Conditions. Sample Time Condition 1 2 3 4 Pressure(psig) 70 70 70 70 Reboiler Temp (° F.) 246.5 246.3 246 246.4 CondenserTemp (° F.) 212.9 212.6 212.1 212.4 Mixed C5 Feed Rate (lb/h) 17.9 18 1818 Overhead Draw Rate (lb/h) 7 7.07 7.06 6.96 H2 Feed to column 201(scfh) 35.17 35.16 35.16 35.16 H2 Feed to column 202 (scfh) 5.09 5.095.09 5.09

TABLE 10 Column 200 Feed Composition Sample Time Condition 1 2 3 4n-pentane 3.865 3.787 3.787 3.787 Isopentane 3.067 3.002 3.002 3.002Cyclopentane 50.877 50.463 50.463 50.463 Cyclopentene 3.769 3.763 3.7633.763 Cyclopentadiene 3.62 3.621 3.621 3.621 Dicyclopentadiene 0.0920.086 0.086 0.086 1-pentene 4.05 4.063 4.063 4.063 Cis-2-pentene 0.7190.723 0.723 0.723 Trans-2-pentene 1.051 1.055 1.055 1.0552-methyl-1-butane 2.145 2.157 2.157 2.157 2-methyl-2-butene 0.886 0.8880.888 0.888 3-methyl-1-butene 0.333 0.332 0.332 0.3322-methyl-1,3-butadiene 9.635 9.671 9.671 9.671 Cis-1,3-pentadiene 1.6542.228 2.228 2.228 Trans-1,3-pentadiene 5.578 5.591 5.591 5.5911,4-pentadiene 2.159 2.167 2.167 2.167 1,2-pentadiene 0.058 0.058 0.0580.058 2,2-dimethylbutane 2.035 2.018 2.018 2.018 Other 4.407 4.327 4.3274.327

TABLE 11 Column 200 Overhead Draw Composition Sample Time Condition 1 23 4 n-pentane 10.289 10.06 10.370 10.601 Isopentane 7.034 7.021 7.1217.244 Cyclopentane 1.092 1.463 1.095 0.929 Cyclopentene 7.220 7.3626.670 6.035 Cyclopentadiene 0 0 0 0 Dicyclopentadiene 0 0 0 0 1-pentene4.689 4.668 4.527 4.482 Cis-2-pentene 7.692 7.705 7.790 7.838Trans-2-pentene 26.986 26.957 27.374 27.594 2-methyl-1-butene 9.0438.929 8.983 9.051 2-methyl-2-butene 20.227 20.048 20.438 20.6333-methyl-1-butene 2.005 2.034 1.903 1.845 2-methyl-1,3-butadiene 0 0 0 0Cis-1,3-pentadiene 0 0 0 0 Trans-1,3-pentadiene 0 0 0 0 1,4-pentadiene0.097 0.1 0.075 0.063 1,2-pentadiene 0 0 0 0 2,2-dimethylbutane 0 0 0 0Other 3.626 3.653 3.654 3.685

TABLE 12 Column 200 Bottoms Draw Composition Sample Time Condition 1 2 34 n-pentane 0.008 0 0.017 0.020 Isopentane 0.001 0 0.007 0.010Cyclopentane 90.882 90.804 90.363 90.013 Cyclopentene 4.652 4.515 4.4324.590 Cyclopentadiene 0.035 0.029 0.030 0.033 Dicyclopentadiene 0.6690.588 0.574 0.594 1-pentene 0.002 0 0.002 0.002 Cis-2-pentene 0.004 00.005 0.006 Trans-2-pentene 0.012 0 0.013 0.014 2-methyl-1-butene 0.0010 0.001 0.001 2-methyl-2-butene 0.016 0 0.018 0.020 3-methyl-1-butene 00 0 0 2-methyl-1,3-butadiene 0.006 0 0.006 0.006 Cis-1,3-pentadiene0.002 0 0.002 0.002 Trans-1,3-pentadiene 0.009 0 0.009 0.0081,4-pentadiene 0 0 0 0 1,2-pentadiene 0 0 0 0 2,2-dimethylbutane 0.3341.114 1.560 1.771 Other 3.367 2.95 2.961 2.910

TABLE 13 Experimental Results Sample Time Condition 1 2 3 4 Linear dieneConversion (wt %) 99.54 99.61 99.65 99.70 Branched Diene Conversion (wt%) 99.97 100 99.97 99.96 Linear Unsaturated Recovery (wt %) 99.12 95.7096.39 95.44 Branched Unsaturated Recovery (wt %) 91.93 91.33 92.14 91.34

From the summary of results in Table 13, it can be concluded that thedual catalyst system according to embodiments herein may provideexcellent catalyst performance, with high selectivity toward the desiredolefin products. In addition, the catalyst system has been tested inpilot plant close to a year, without showing observable catalystdeactivations, the catalyst system thus being very stable and robust inthe catalytic distillation reactor system. While the cyclopenteneconcentration in the overheads of the pilot plant system was relativelyhigh, more distillation stages above the catalyst bed or an ensuingcyclopentene removal column may be used to reduce cyclopentene level toa desired level.

As described above, embodiments disclosed herein relate generally toprocesses and systems for the production of linear C5 olefins from C5feeds, such as steam cracker C5 feeds and FCC C5 feeds. Moreparticularly, embodiments disclosed herein relate to processes forproducing C5 olefins via catalytic distillation reaction systems, thecatalytic distillation reaction system including a bed of hydrogenationcatalyst for converting C5 dienes to C5 olefins, among other reactions.

Control of the catalytic distillation reaction system is complex. Inaddition to the need to control overhead cyclopentene and dieneconcentrations, the process is complicated by several additionalfactors: the C5s are relatively close boiling; one or more of thereaction zones may require an amount of diluent or inert compounds toaid in heat removal; feed composition variations; weather changes;hydrogenation catalyst activity changes; and other various processdisruptions and variables that may be encountered, affecting not onlyproduct purity, but energy usage and olefin recovery efficiency.

Typical process control for a distillation column may includetemperature control. For example, for a typical temperature controllerin a distillation tower, a temperature on a selected tray is controlledby adjusting distillation process variables, such as heat input to thecolumn reboiler. However, it has been found very difficult to controland/or optimize a C5 selective hydrogenation column (a C5 catalyticdistillation reaction system for selectively hydrogenating C5 dienes ina mixed C5 feed) using a typical temperature control scheme. Because ofthe relatively close boiling points of the C5 olefins, cyclopentene, andcyclopentane, the temperature profile along the catalytic distillationreactor system is relatively flat. Thus, minor changes in temperaturecan shift the concentration of various C5 components within the column.It has been found that these shifts may negatively impact the catalystzones, and that the C5 olefin recovery can be quickly deteriorated.

It has been found that improved control of the catalytic distillationreactor system and increased olefin recovery may be achieved bycontrolling a concentration profile of a selected inert compound orcompounds within the catalytic distillation reactor system. In someembodiments, the selected inert compound may be an added diluent, suchas a C5, C6, or C7 hydrocarbon, a diluent or inert compound present inthe C5 feedstock, or a diluent formed in situ, such as via hydrogenationof cyclopentene to form cyclopentane. The selected inert compound shouldhave a boiling point greater than a boiling point of the target overheadproduct, such as 1-pentene or 2-pentene, and in some embodiments mayhave a boiling point or range intermediate that of the lowest andhighest boiling compounds in the column feed. Additionally, the selectedinert compound is preferably not a reactive component fed to thecatalytic distillation reaction system, such as a pentadiene, a productof the selective hydrogenation, such as 1-pentene or 2-pentene, or avery minor component in the mixed hydrocarbon feedstock. The high orintermediate boiling point or range and concentration of the selectedinert compound(s) may thus allow for a reliable presence at a measurableconcentration at one or more elevations within the column. While areactive or minority component may be used, such compounds are subjectto column dynamics, and may not be a reliable source for control.

For example, it has been found that improved control of the catalyticdistillation reactor system may be achieved by controlling acyclopentane concentration profile within the catalytic distillationreactor system. Alternatively, improved control of the catalyticdistillation reactor system may be achieved by controlling a combinedcyclopentene and cyclopentane concentration profile within the catalyticdistillation reactor system. In this manner, the cyclopentane andcyclopentene in the catalyst beds may be controlled to prevent theconcentration of the inert compounds from becoming too low, thusreducing the C5 olefin recovery, or too high, thus contaminating the C5olefin product with cyclopentene. Maintaining a proper concentrationprofile of cyclopentane and cyclopentene throughout the catalyst zoneshas been found effective at providing the desired column control,hydrogenation performance, separation, and olefin recovery. Maintainingan appropriate cyclopentane and/or cyclopentene concentration profilewithin the column may maximize C5 olefin recovery and C5 dieneconversion while at the same time control the cyclopentene content inthe C5 olefin overhead product stream.

The concentration profile may be controlled by measuring at least one ofa composition and a density at one or more column elevations. The methodfor measuring composition or density may be selected based onrobustness, reliability, cost, ease of implementation, and other factorsrelated to the process and site. As used herein, “column elevation”refers to a sample or measurement point, such as a measurement taken ona vapor or liquid within the column, i.e, between the lowermost stageand uppermost stage of the column, including the overhead (stream 20 inFIG. 8 (described below), for example), but not including the overheadliquid draw (stream 25 in FIG. 8, for example).

In some embodiments, the concentration profile of a selected inertcompound within the column may be measured and controlled by use of anon-line gas chromatograph (GC). For example, a PGC2000 E2 on-line gaschromatographs, available from ABB Inc., Wickliffe, Ohio, may be used tomeasure discrete hydrocarbons in a mixed hydrocarbon stream. The GC mayanalyze a sample from one or more column elevations, where the samplemay be a gas phase sample or a liquid phase sample. For example, the GCmay analyze a sample from one or more elevations to determine aconcentration of cyclopentane and/or cyclopentene at the elevation or aconcentration profile of cyclopentane and/or cyclopentene within thecolumn. Column variables may then be adjusted to control the columnelevation(s) at or near the target concentration. For example, in oneembodiment, one or more sample analyzers may be cascaded with flowcontrollers to control one or more of overhead draw rate and reboilerheat input, among other variables.

In other embodiments, the concentration profile of a selected inertcompound within the column may be controlled by measuring andcontrolling a liquid density at one or more column elevations. A densitymeasurement device or density meter may be disposed in a downcomer orliquid re-distribution point within the column, where a directmeasurement of density may be made. Alternatively, density may beindirectly measured via a density profiler, such as a gamma raybackscatter density profiler disposed adjacent the column to measure adensity of fluids, such as in a downcomer, within the column. Frothingof the liquids in a downcomer or elsewhere within the column may disruptdirect measurement, whereas a density profiler may be able to directlyaccommodate varying froth levels; nonetheless, both systems may havetheir advantages and disadvantages. Column variables may then beadjusted to control the column elevation(s) at or near the targetdensity. For example, in one embodiment, one or more density analyzersmay be cascaded with flow controllers to control one or more of overheaddraw rate and reboiler heat input, among other variables.

Density control indirectly controls the concentration profile of thetarget inert compound within the column. The specific gravity of pentaneis about 0.64, 1,3-pentadiene 0.683, cyclopentane 0.751, andcyclopentene 0.771. Density may be related to composition (e.g., thedensity of the mixture is a function of the concentration or massfraction of the various components in the mixture, temperature andpressure, oversimplified, for example, as ρ_(mix)=f([pentene],[cyclopentene], [pentadiene], [cyclopentane], T, P)). At column pressureand elevation temperature, the density of the mixture may thus be usedto control a concentration of the inert diluent. Knowing therelationship between density and composition, one skilled in the art maythus be able to use density as an indirect means for compositioncontrol—as the composition becomes heavier, the concentration ofcyclopentene and cyclopentane at the elevation is increasing, and as thecomposition becomes lighter, the concentration of cyclopentene andcyclopentane at the elevation is decreasing.

When measuring density, the control scheme may be based on density orcomposition. As noted above, density is an indicator of composition. Insome embodiments, a density set point may be used as a control basis. Inother embodiments, a concentration set point may be used as a controlbasis, where the composition is determined based on the measureddensity.

Inert or diluent compounds that may be selected as a control basis mayhave a boiling point or boiling range of greater than about 100° F., forexample, so as to preferentially remain in the lower portions of thecolumn and not be collected with the overhead fraction in anysignificant content, the target olefins, 1-pentene and 2-pentene havinga normal boiling point lower than the inert or diluent compoundsselected. In some embodiments, the inert or diluent compounds selectedas a control may have a boiling range or boiling point in the range fromabout 100° F. to about 125° F., such as from about 102.5° F. to about122.5° F. or from about 111° F. to about 121° F.

Inert or diluent compounds that may be selected as a control basis mayhave a specific gravity of greater than about 0.675, for example, so asto distinguish over the lower density target olefins and allow anoperator or control system to determine a response to changes inmeasured density. In some embodiments, the inert or diluent compoundsselected as a control may have a specific gravity in the range fromabout 0.675 to about 0.9, such as from about 0.7 to about 0.8 or fromabout 0.73 to about 0.78.

When controlling based upon diluent compound concentration, one or morecolumn operating parameters may be adjusted to maintain a set pointconcentration. For example, a controller may be configured to performone of the following actions: decrease an overhead flow and increase areflux flow when a diluent compound concentration profile starts to moveup the column and the reflux flow is below a column flooding value;increase an overhead flow and decrease reflux flow when a diluentcompound concentration profile starts to move down the column and thereflux flow is above a minimum design value (e.g., where the reflux isenough to wet the catalyst, dissipate the reaction heat, and removecyclopentene from the C5 olefins); decrease a reboiler duty (if thereflux flow needs to be maintained a constant value) and an overheadflow when the diluent compound concentration profile starts to move upthe column; or, increase a reboiler duty (if the reflux flow needs to bemaintained a constant value) and an overhead flow when the diluentcompound concentration profile starts to move down the column.

When controlling based upon density, one or more column operatingparameters may be adjusted to maintain a set point density. For example,a controller may be configured to perform one of the following actions:decrease an overhead flow and increase a reflux flow when a densityprofile indicates a concentration of a target compound is starting tomove up the column and the reflux flow is below a column flooding value;increase an overhead flow and decrease a reflux flow when a densityprofile indicates a concentration of a target compound is starting tomove down the column and the reflux flow is above a minimum design value(e.g., where the reflux is enough to wet the catalyst, dissipate thereaction heat, and remove cyclopentene from the C5 olefins); decrease areboiler duty (if the reflux flow needs to be maintained a constantvalue) and an overhead flow when the density profile indicates aconcentration of a target compound is starting to move up the column;or, increase a reboiler duty (if the reflux flow needs to be maintaineda constant value) and an overhead flow when the density profileindicates a concentration of a target compound is starting to move downthe column.

The above are one envisioned manner to meet the target objective ofmaintaining an appropriate concentration profile of the diluent compoundwithin the column, which may aid in one or more of maximizing C5 olefinrecovery, maximizing C5 diene conversion, and controlling cyclopentenein the C5 olefin product stream. Other control schemes, as well asadjustment of other process variables, may also be employed to meet theobjectives of improved control and process efficiency.

Referring now to FIG. 8, a simplified flow diagram of a process forproducing C5 olefins from a mixed hydrocarbon stream according toembodiments herein is illustrated. A C5-olefin containing stream 10,such as described above and containing linear pentenes, dienes,acetylenes, cyclopentane, and cyclopentene, and a hydrogen stream 12 maybe fed to a catalytic distillation reactor system 14. Catalyticdistillation reactor system 14 may include one or more reaction zonesabove the C5 feed elevation, and/or one or more reaction zones below theC5 feed elevation. As illustrated, catalytic distillation reactor system14 includes two reaction zones 16, 17 disposed above the C5 feedelevation and one reaction zone 18 disposed below the C5 feed elevation.Hydrogen 12 may be introduced to the column below the lowermost reactionzone, zone 18, or may be split fed below two or more of the reactionzones.

In catalytic distillation reactor system 14, acetylenes and dienes inthe C5 feed are selectively hydrogenated over a hydrogenation catalyst,converting the acetylenes and dienes to olefins. Some olefins may alsobe converted to paraffins, but catalyst selectivity, hydrogenconcentrations, and reaction zone temperatures may be maintained tolimit olefin hydrogenation, selectively hydrogenating the more reactivedienes and acetylenes. Concurrent with the selective hydrogenation, theC5 feed is fractionated into an overheads fraction 20, including theolefins, and a bottoms fraction 22, including heavier or higher boilingfeed components, such as unreacted dienes as well as cyclopentene andcyclopentane.

A portion of the bottoms fraction 22 may be vaporized in reboiler 23 andreturned to column 14, and a remaining portion of the bottoms fraction22 may be recovered as a bottoms product 24. The overhead fraction 20may be condensed, a portion of the condensed overheads being returned tocolumn 14 as a reflux, and a remaining portion being recovered as anoverhead product fraction 25.

As noted above, it is desired to limit a content of dienes andcyclopentene in overhead product fraction 25. It is also desired tomaintain stable column operations, even though the column may have arelatively flat temperature profile, while meeting the overheadspecifications and maximizing C5 olefin recovery and C5 dieneconversion. The column may include one or more sample points 19 forwithdrawing and feeding a liquid sample or a vapor sample to an analyzer21, such as a gas chromatograph (GC) for determining a concentration ofcyclopentene and/or cyclopentane in the column at the sample pointelevation.

As illustrated in FIG. 8, column 14 includes one sample point 19disposed intermediate the upper reaction zone 17 and lower reaction zone18, as well as below the C5 feed point elevation. Additional oralternative sample locations may be used, and may be fed to separateanalyzers or a single analyzer capable of serial or parallel analyses.

The elevation of the sample point may be selected based on columndynamics estimated for a particular feedstock and reaction zoneconfiguration. For example, it may be determined, via simulation orsampling for example, that a change in concentration of cyclopentane isapproximately at a peak value within the column at a particularelevation. A sample point may be located proximate that elevation, suchas within a few stages or equivalent heights of packing for example. Asused herein, proximate an elevation refers to being within a fewdistillation stages, such as within about 5 or 10 stages for a columnhaving 100 stages, for example, where stage or distillation stage refersto actual distillation trays or an equivalent (theoretical or otherwise)height of packing. Thus, where a desired sample point is determined tobe approximately at stage 85, a sample point may be located betweenstages 80 and 90, for example. The actual sample elevation may dependupon several factors, including accessibility at the desired elevation.Preferably, the sample point is not located proximate an elevation wherea change in concentration of the control compounds is small within thecolumn, as this may hamper the ability of a control system to properlycontrol the column, the concentration decreasing regardless ofdirection, making determination of the action to be taken difficult asit cannot readily be determined if the concentration profile is movingup or down the column.

The GC may then analyze the sample to determine a concentration ofcyclopentene and/or cyclopentane at the sample elevation. The samplingresult, such as a summation of the cyclopentane and cyclopenteneconcentrations, may then be provided to a controller 13, such as adigital control system or other types of control systems known in theart. Controller 13 may be a flow indicator controller (FIC) configuredto control the overhead flow control loop, including flow meter 27 andflow control valve 29, to maintain a desired set point concentration ofcyclopentane at the sample elevation. If the summation of cyclopentaneand cyclopentene profile starts to move up the column, the overhead flowcan be reduced (i.e., reflux flow may need to be increased) and allowmore flow to the bottom stream, while if the cyclopentane andcyclopentene profile starts to move down the column, the overhead flowcan be increased (i.e., reflux flow may need to be decreased) and at thesame time reduce column bottom flow.

C5 diene hydrogenation is highly exothermic and enough reflux flowshould be maintained to wet the catalyst and prevent reaction run away,and hence for some cases, such as for steam cracker C5 feeds having highconcentrations of dienes, it may be more beneficial to keep a constantreflux flow to the column. In such an instance, it may be morebeneficial to vary reboiler duty to either decrease or increase overheadflow if the cyclopentane and cyclopentene concentration profile startsto move up or down, such as illustrated in FIG. 9, rather than simplyincrease more overhead flow by reducing reflux flow. As illustrated inFIG. 9, where like numerals represent like parts, the sampling result,such as a summation of the cyclopentane and cyclopentene concentrations,may be provided to a controller 28. Controller 28 may be a heatindicator controller (HIC) configured to control heat input to thereboiler, such as by varying a flow, pressure, or temperature of a heatexchange fluid, such as steam or water, provided to the reboiler.

Embodiments disclosed herein may include systems having one or moresample points. FIGS. 8 and 9 include a single sample point at anelevation between the upper and lower catalyst beds and below the feedpoint. For very tall columns, such as where the rectification andstripping portions of the column may be split into two columns linked tooperate as a single distillation column, a sample point may be disposedwithin or proximate the mid-reflux stream or mid-reboil stream.Additional sample points may be disposed at other locations along thecolumn, including below, intermediate, or above reaction zone(s) locatedin the rectification and stripping portions of the column, in theoverhead vapor draw, in the overhead product draw, in the bottoms liquiddraw, and/or in the bottoms product draw. These additional sample pointsmay be used to monitor performance of the column, and/or may be used toprovide additional inputs to the control system. For example, asillustrated in FIGS. 10 and 11, where like numerals represent likeparts, additional analyzers 2, 4, 6 may be used to determine theconcentration of cyclopentene and/or cyclopentane in the overheadproduct draw 25, the bottoms product draw 24, and below the lowercatalyst zone 18, respectively. Sample analysis results from one or moreof analyzers 2, 4, 6 may be used to monitor system performance based oncontrolling of the system via the concentration profile determined viaanalyzer 21; alternatively or additionally, one or more of analyzers 2,4, 6 may be used as an input to controller 13, 28 to enhance the controlof the system and effect the desired concentration profile within thecolumn. Such embodiments may further the enhancement in conversion ofdienes and recovery of olefins via concentration profile control.

As described above with respect to FIGS. 8-11, analyzers, such as GCs,may be disposed and used for measurement of concentrations at variouscolumn elevations. One or more of analyzers 21, 2, 4, 6 may be a densityanalyzer or density measurement device. For example, as illustrated inFIG. 12, distillation column reactor system 14 may include one or moredensity measurement devices 70 disposed within a downcomer 72. Forexample, a density sensor, such as one using an oscillating U-tubeprinciple, may be used. An output from the density measurement devicemay then be communicated to a controller 13, 28 (FIGS. 8-11) for controlof the column based upon the density profile or a concentration profiledetermined based on the density profile. As another example, such asillustrated in FIG. 13, distillation column reactor system 14 mayinclude one or more gamma ray backscatter density profilers 74 that maybe used to measure a density of the fluids within a downcomer 72. Forexample, a density profiler such as described in US20130123990 (ThermoFisher Scientific Inc., Sugarland, Tex.) may be used. Gamma rays emittedfrom source 76 and backscattered to detector 78 may be used to determinea density of the fluid in the downcomer. An output from the detector 78may then be communicated to a controller 13, 28 (FIGS. 8-11) for controlof the column based upon the density profile or a concentration profiledetermined based on the density profile.

Referring again to FIGS. 1-4, in catalytic distillation reactor system44, the C5 olefin-containing feed is concurrently fractionated andselectively hydrogenated, where control of the catalytic distillationreactor system may include a control scheme as described above withrespect to one or more of FIGS. 8-13 via an analyzer 51, such as a GC ordensity measurement device. Control of the concentration profile viaanalyzer 51 and as described above with respect to FIGS. 8-13 may thenbe used to enhance the performance of the column and conversion ofdienes within reaction zone 46.

While described above with respect to selective hydrogenation of C5s,control of catalytic distillation reactor systems via controlling adensity profile or a concentration profile of a selected non-keycomponent may be extended to other mixed hydrocarbon feeds. For example,processing of close boiling C4 fractions, C6 fractions, C7 fractions,and the like in a catalytic distillation reactor system may benefit fromdensity or concentration profile control, enhancing the performance ofsuch catalytic distillation reactor systems with respect to reactionzone efficiency and product recovery efficiency. Such catalyticdistillation reactor systems may be used for dimerization,oligomerization, hydrogenation, desulfurization, isomerization,etherification, dehydrogenation, back cracking, disproportionation,transesterification, or other various reactions known to benefit fromLeChatalier's principle via concurrent reaction and separation.

Example 4

Simulations were conducted to give an example of how to determine theappropriate sample locations of a catalytic distillation reactor systemfor selectively hydrogenating a C5 feed stream. The C5 feed compositionis shown in Table 14. Simulations were carried out in ASPEN PLUS 7.3.2(Aspen Technology, Inc., Burlington, Mass.). The reactions considered inthe simulation are provided in Table 15. Simulations for columns wereperformed with the column configurations in Table 16. Two simulationswere performed to check the effect of bottom flow rate on change oftotal inert and a summation of cyclopentene and cyclopentane along thecolumn.

TABLE 14 C5 Feed Composition to C5CDhydro column (wt. %) ISOBUTYLENE0.0022% 1-BUTENE 0.0005% N-PENTANE 5.3794% 2-METHYL-BUTANE 4.4459%CYCLOPENTANE 40.8229%  CYCLOPENTENE 5.4332% CYCLOPENTADIENE 4.1475%DICYCLOPENTADIENE 0.1046% 1-PENTENE 5.1483% CIS-2-PENTENE 1.3293%TRANS-2-PENTENE 2.6058% 2-METHYL-1-BUTENE 2.1779% 2-METHYL-2-BUTENE3.4958% 3-METHYL-1-BUTENE 0.4424% 2-METHYL-1,3-BUTADIENE 9.8304%CIS-1,3-PENTADIENE 3.2129% 1-TRANS-3-PENTADIENE 6.7781% 1,4-PENTADIENE2.7135% 1,2-PENTADIENE 0.0663% N-HEXANE 0.0691% 2-METHYL-PENTANE 0.0462%3-METHYL-PENTANE 0.0537% 2,2-DIMETHYL-BUTANE 1.6329% 2-ETHYL-1-BUTENE0.0011% BENZENE 0.0023% Others 0.0581%

TABLE 15 Reactions considered in the Aspen Plus simulation1-TRANS-3-PENTADIENE + HYDROGEN --> TRANS-2-PENTENE CIS-1,3-PENTADIENE +HYDROGEN --> CIS-2-PENTENE 1,2-PENTADIENE + HYDROGEN --> TRANS-2-PENTENE1,4-PENTADIENE + HYDROGEN --> TRANS-2-PENTENE 2-METHYL-1,3-BUTADIENE +HYDROGEN --> 2-METHYL-2- BUTENE CYCLOPENTADIENE + HYDROGEN -->CYCLOPENTENE

TABLE 16 Simulation Conditions Case Number 1 2 Column Stages 102 102 C5Feed Stage 72 72 Hydrogen Feed Stage 95 95 Reaction Zone Stages 60-7060-70 73-82 73-82 Pressure (psia) 135 135 Reflux Ratio 7.5 7.5 C5 Feedrate (lb/h) 17999.0 17999.0 H2 feed rate (lb/hr) 300.53 300.53 Bottomsrate (lb/hr) 9358.3 9561.7

FIG. 14 illustrates the concentration profile for cyclopentene pluscyclopentane within the column for Simulation Condition 1. Theconcentration of cyclopentene and cyclopentane increases slowly movingfrom the top of the column (stage 1) downward, increases significantlywithin the catalyst beds, and then leveling off closer to the bottombetween stages 90 and 102. FIG. 15 is a graph depicting the change inthe concentration profile for cyclopentane plus cyclopentene after thecolumn reaches equilibrium at the conditions for Simulation Condition 2.

It can be seen from FIGS. 14 and 15 that after increasing the bottomsdraw rate from 9358.3 lb/h to 9561.7 lb/h, a noticeable change in thesummation of cyclopentane and cyclopentene (above 5%) occurs from stage46 to stage 96, and the change is at an approximate peak value at stage85. This suggests that a good sample point may thus be located betweenstages 80 and 90, for example, for determining whether or not theconcentration profile is moving up or down the column. However, thisdoesn't rule out additional sample points in column overhead stream,mid-reflux stream, and bottom stream because these three streams aretypically easily accessible.

FIG. 16 illustrates the temperature profile within the column forSimulation Conditions 1 and 2. As can be seen, there are only minorchanges in the column temperature profile after increasing column bottomflow rate from 9358.3 lb/h to 9561.7 lb/h. From this result, it can beappreciated that temperature control for C5CDHydro column may bedifficult. As described below, pilot plant experiments confirmed thisresult.

Example 5: Experimental Example

Steam cracker C5 dienes selective hydrogenation over a palladiumcatalyst (about 0.6 wt % palladium on a support) and a nickel-basedcatalyst (about 33.3 wt % nickel oxide on a support) were studied in apilot plant. The objective of the pilot plant experiments was to reducedienes from very high levels down to a very low level while minimizingthe loss of unsaturates. In particular linear olefin recovery wasconsidered more important than iso-olefin recovery because, in adownstream of methathesis unit, one mole linear C5 olefin cantheoretically produce three moles of propylene, while one mole ofbranched C5 olefin can produce one mole of propylene. Two pilot plantconfigurations were used, the first corresponding to FIG. 17 (feedpurification) plus FIG. 18 (composition based control similar to theembodiment of FIG. 8), the second corresponding to FIG. 17 plus FIG. 19(composition based control similar to the embodiment of FIG. 9)

Referring now to FIG. 17, C5 feed purification was performed by feedinga pygas 100 and a cyclopentane stream 102 to a distillation column 104.Column 104 was entirely filled with Raschig super rings. The aromaticsand C6+ hydrocarbons were separated as bottom product 106 while the C5hydrocarbons were recovered in the overhead stream 108. The overheadproduct stream was then used as a feed to the catalytic distillationreactor systems described below with respect to FIGS. 18 and 19.

The catalytic distillation reactor systems 200 of FIGS. 18 and 19 aresimilar, column 200 being split into a stripping section 201 and arectifying section 202. The stripping section 201 (below the elevationof feed 108 introduction) includes one reaction zone 204 containing aselective hydrogenation catalyst, and the rectifying section (above theelevation of feed 108 introduction) includes tow reaction zones 206, 208containing a selective hydrogenation catalyst. Hydrogen 210, 212 isintroduced below reaction zones 204, 206, respectively. Dienes in feed108 are converted within column 200 to olefins and recovered in thedistillate product 216. The catalyst zones 206, 208 above the feed wereused to convert light dienes such as isoprene and cyclopentadiene.Heavier linear dienes traverse down and were reacted in catalyst zone204 to prevent significant yield loss to the bottoms product 218.Rectifying section 202 was charged with 8 ft of Raschig super rings atthe top followed by 14 ft of palladium catalyst and 7 ft of nickelcatalyst. Stripper section 201 was filled with 6 ft of Raschig superrings at the top followed by 7 ft of nickel catalyst and 18 ft ofRaschig super rings.

Referring now to FIG. 18, column 200 is configured for cyclopentane pluscyclopentene composition profile control, where an analyser 220 isdisposed in the mid-reflux line 222. The control system is configured tocontrol the composition profile via adjustment of the draw rate ofoverhead product stream 216 (i.e., column overhead flow control is usedto optimize the cyclopentane and cyclopentene profile in the mid-refluxstream). Based on an output from analyser 220, the flow control loop 215on the overhead draw, including flow meter 217 and control valve 219, isadjusted. When the summation of cyclopentane and cyclopentene increasesand deviates from the set-point, the overhead flow is reduced while thereflux flow is increased (i.e., cascaded to overhead drum level). Whenthe summation of cyclopentane and cyclopentane becomes less than the setpoint, the overhead flow is increased which at the same time the refluxflow is decreased (i.e., cascaded to overhead drum level).

Referring now to FIG. 19, column 200 is also configured for cyclopentaneplus cyclopentene composition profile control, where an analyzer 220 isdisposed in the mid-reflux line 222. The control system 225 isconfigured to control the composition profile via adjustment of the heatinput to reboiler 224 (i.e., reboiler heat input is used to optimize thecyclopentane and cyclopentene profile in the mid-reflux stream). Columnreflux flow is kept constant via flow control loop 230 (including flowmeter 232 and control valve 234) and the overhead draw rate is allowedto vary based on level control in drum 226, where the level controller238 is cascaded to flow control loop 240 (including flow meter 242 andcontrol valve 244). For example, when the cyclopentane profile moves upand away from the set point, the reboiler duty is decreased and henceless liquid is accumulated in the overhead drum 226. The overhead flowis cascaded to the overhead drum level and thus the overhead flow isreduced while the reflux flow is maintained at the same rate.

FIG. 20 provides a summary of the pilot plant data, including themeasured linear/branched C5 olefin recovery rate, C5 diene conversionand cyclopentene concentration in the overhead stream plotted againstthe summation of cyclopentane and cyclopentene measured in themid-reflux stream. It can be seen that below about 50 wt % ofcyclopentane and cyclopentene concentration in the mid-reflux stream,either linear or branched C5 olefin recovery and diene conversiondeteriorated significantly. Above around 50 wt % of cyclopentane andcyclopentene concentration in the mid reflux stream, either branched orlinear C5 olefin recovery starts to level off. There is almost a linearrelationship between the cyclopentene concentration in the overheadstream vs. the total cyclopentane and cyclopentene in the mid refluxstream.

The pilot plant runs illustrate that a composition profile control maybe used to operate a column at close to 100% diene conversion (hencevery little or no diene will be present in the C5 olefin product stream)while maximizing C5 olefin recovery rate (typically higher than ˜90%)and at the same time controlling cyclopentene concentration in theoverhead C5 olefin product. While the cyclopentene concentration in theoverheads of the pilot plant system was a little higher than the desired0.5 wt %, more distillation stages above the catalyst bed or an ensuingcyclopentene removal column may be used to reduce cyclopentene level.

As described above, various embodiments may include a heat soaker 32. Insome embodiments, however, a heat soaker is not required, as will bedescribed below. Typically, in prior art processes, the above notedproblems associated with steam cracker C5 feeds or similar feedstockscontaining relatively high amounts of highly reactive species are solvedby use of a heat soaker, also known as a dimerization reactor, todimerize the cyclopentadiene and form dicyclopentadiene. This reactionoccurs before any initial separator or partial hydrogenation unit. Heatsoakers, from an energy standpoint, are costly to operate and requirethe use of additional supporting equipment.

The effluent from the heat soaker, which will include linear andbranched C5 olefins, linear and branched C5 dienes, dicyclopentadiene,cyclic C5 olefins, and other C6+ hydrocarbons, among others, is thentypically fed to a convention distillation column operated in mixedliquid/vapor flow. In the distillation column, C6+ hydrocarbons,including dicyclopentadiene, are separated from the linear, branched,and cyclic C5 olefins. As noted, this method of cyclopentadiene removalis energy intensive and requires additional process equipment.

Alternatively, it has been found that the use of a distillation columnoperated in liquid continuous mode may advantageously replace theconventional distillation column operated in mixed liquid/vapor mode.Due to the liquid continuous mode, improved mixing, and improved heatprofile, it has also been found that cyclopentadiene may undergo DielsAlder reaction in the distillation column to dimerize thecyclopentadiene and form dicyclopentadiene. As a result, the heat soakermay also be removed while retaining the dimerization function.

Accordingly, embodiments disclosed herein relate to an improved processfor producing C5 olefins with limited cyclopentadiene and other dienesin the product stream without the need for expensive heat soakers ordimerization reactors. Eliminating a heat soaker and replacing theconventional distillation column with a liquid continuous distillationcolumn may allow for the reduction in process equipment, lower operatingcost, and simplicity of operation while retaining the dimerizationfunction of the heat soaker.

FIG. 21 illustrates an improved process for producing C5 olefins from amixed hydrocarbon stream utilizing a liquid continuous distillationcolumn for the concurrent dimerization and removal of cyclopentadiene.According to embodiments disclosed herein, hydrocarbon stream 35, suchas a steam cracker C5 feed, may contain cyclopentadiene, linear andbranched C5 olefins, linear and branched C5 dienes, cyclic C5 olefins,and C6+ hydrocarbons, among other components as described above. Mixedhydrocarbon stream 34 may be fed to a low temperature/low pressuredistillation column 36, such as a bubble type distillation columnoperating in liquid continuous mode. In the distillation column,cyclopentadiene is dimerized to form dicyclopentadiene. Additionally,cyclopentadiene may be reacted with other compounds, such as isoprene,to form heavy olefin compounds.

Concurrently, distillation column 36 may also fractionate the mixedstream to form a bottoms fraction 40 containing the C6+ hydrocarbons,dicyclopentadiene, and other heavy components, and an overheads fraction38 containing the linear, branched, and cyclic C5 olefins, and thelinear and branched C5 dienes. Any sulfur compounds contained in themixed hydrocarbon stream may also be recovered with bottoms fraction 40.To obtain the desired separation, distillation column 36 may becontrolled to limit the overhead fraction benzene content to less than0.5 wt %, for example.

The overhead fraction 38 may then be recovered and fed to a catalyticdistillation reactor system 44 and processed as described above.

The distillation column 36 may be a low temperature/low pressureseparator, such as a distillation column operated in liquid continuousmode. The column may be operated at a pressure in the range from about15 psia to about 85 psia, such as from about 20 psia to about 80 psia orfrom about 25 to about 75 psia, and at a condenser temperature in therange from about 90° F. to about 150° F., such as from about 110° F. to145° F. or from about 120° F. to about 135° F. As noted above,distillation column 36 may be controlled, such as via reflux rate anddistillate to feed ratio, to minimize the amount of sulfur containingcompounds and benzene in lower boiling fraction 38, and to minimize theamount of valuable olefins and dienes (to be converted to olefinsdownstream) recovered with higher boiling fraction 40. The residencetime in the liquid continuous distillation column should be sufficientto convert the cyclopentadiene to dicyclopentadiene, while limiting thethermal reaction of other components, as the dienes may be converted todesirable olefins in reactor system 44, as described above. Theresidence may in the range of about 0.2 hours to about 6 hours, such asin the range from about 1.5 hours to about 3 hours. In some embodiments,the dimerization reaction conditions of temperature, pressure, andresidence time are controlled to achieve at least 90% conversion of thecyclopentadiene, such as at least 92%, at least 93%, at least 93% or atleast 94% cyclopentadiene conversion to heavier compounds, such asdicyclopentadiene. Various manners of operating such a liquid continuousdistillation column are described in U.S. Pat. No. 7,287,745, hereinincorporated by reference. Advantageously, it has been found that aliquid continuous distillation column in C5 service may effectivelyoperate as both a heat soaker and separator.

Example 6

Simulations were conducted to compare the performance of systems forselectively hydrogenating a C5 feed stream according to variousembodiments herein. Simulations were carried out in ASPEN PLUS 7.2(Aspen Technology, Inc., Burlington, Mass.).

In this Example, a process similar to that as illustrated in FIG. 21 issimulated. In the simulations, dienes and acetylenes are assumed to beselectively hydrogenated into olefins in the catalytic distillationreactor system, and all olefins are assumed to be saturated into alkanesin the total hydrogenation unit. Process conditions were as follows.

TABLE 17 Process Conditions for Example 1 Case# 1 Low P/T columnPressure, psia 27 Column stages 30 Condenser temp, ° F. 130 Reboilertemp, ° F. 259 Feed stage 14 Dimerization/Liquid continuous 10-30Thiophene in distillate, ppm 0 Benzene in distillate, wt % 0.5 wt % C5olefin recovery, %   100% C5CDHydro column Column stages 102 C5 feedstage 42 H2 feed stage 60 Hydrogenation reaction zone 30-40 43-50Cyclopentene in OVHD, wt %  0.46% Linear olefin recovery, % 89.95% Totalolefin recovery, % 89.44% Pressure, psia 135 Mass reflux molar ratio10.68 Bottom vs. feed molar ratio 0.442 PPH2, psi 15.6 TotalHydrogenation Unit Pressure, psia 260 Temperature, ° F. 230 PPH2, psi181 Recycle vs. feed molar ratio 0.81

The simulated mass balance for Example 6 is shown in Table 18.

TABLE 18 Low PT Col Low PT Col Recycle CDHydro CDHydro Mass Flow lb/hrPygas Feed OVHD STMs stream HTU PRO OVHD purge Vent Loss C4s 46.29 46.290.00 0.00 0.00 27.21 0.00 19.07 N-PENTANE 576.77 576.76 0.01 4.16 32.90553.04 1.02 51.21 2-METHYL-BUTANE 641.04 641.04 0.00 0.00 65.47 616.550.00 89.96 CYCLOPENTANE 89.64 83.90 5.75 2532.15 3116.81 0.55 608.030.01 CYCLOPENTENE 651.19 645.85 5.532 509.58 0.00 26.69 119.55 1.85CYCLOPENTADIENE 6718.23 15.79 0.00 0.00 0.00 0.00 0.00 0.00DICYCLOPENTADIENE 0.00 0.00 6701.44 21.94 21.94 0.00 5.15 0.00 1-PENTENE719.41 719.40 0.01 0.00 0.00 637.80 0.00 81.60 CIS-2-PENTENE 118.40118.38 0.02 14.96 0.00 646.76 3.51 57.20 TRANS-2-PENTENE 193.38 193.350.03 12.78 0.00 1383.18 0.00 125.03 2-METHYL-1-BUTENE 448.22 448.21 0.010.01 0.00 398.90 0.00 49.31 2-METHYL-2-BUTENE 0.00 0.00 0.00 63.63 0.001679.57 14.93 129.88 3-METHYL-1-BUTENE 60.89 60.89 0.00 0.00 0.00 50.130.00 10.76 2-METHYL-1,3-BUTADIENE 1834.04 1433.69 0.35 0.00 0.00 0.000.00 0.00 CIS-1,3-PENTADIENE 591.99 586.08 5.31 0.00 0.00 0.00 0.00 0.001-TRANS-3-PENTADIENE 940.42 935.02 4.80 0.00 0.00 0.00 0.00 0.001,4-PENTADIENE 347.86 347.86 0.00 0.00 0.00 0.00 0.00 0.001,2-PENTADIENE 9.02 8.91 0.11 0.00 0.00 0.00 0.00 0.00 BENZENE 19148.8839.92 19108.97 32.33 0.00 0.00 7.58 0.00 C6+ 22864.32 684.39 22179.243111.04 3156.37 0.00 729.75 0.00 HYDROGEN 0.00 0.00 0.00 0.00 68.29 1.100.00 457.90 Total flow 55999.99 7987.73 48012.27 6362.78 6462.78 6021.481492.51 1073.80

As can be seen in Table 18, substantially all of the cyclopentadiene inthe feed gas (6718.23 lb/hr) is dimerized to dicyclopentadiene andremoved in the column bottoms (6701.44 lb/hr). Only a small portion ofcyclopentadiene remains in the column overheads (16.79 lb/hr), equatingto a 99.75% conversion. Additionally, substantially all of the linearand branched olefins are recovered from the column overheads.

Advantageously, embodiments herein provide an efficient and effectivemeans for recovering C5 olefins from steam cracker C5 cuts. In someembodiments, a dual catalyst system, including a nickel-based catalystand a palladium-based catalyst, has been found to be highly selectivetoward the desired olefin product, provide a high olefin recoverypercentage, and to be very robust. In other aspects, it has been foundthat controlling a composition profile of an inert or diluent compoundwithin a catalytic distillation reactor system may be used to optimizereaction within the catalyst beds as well as product recovery andpurity.

Embodiments herein are described as useful for processing of streamcracker C5 feeds. Similar C5 cuts containing relatively high amounts ofhighly reactive species may also be processed according to embodimentsherein. However, due to the relatively low level of highly reactivespecies typically found in an FCC cut, processes related to FCCfeedstocks may not be viewed as relevant, as one skilled in the artwould not look toward processing of such feeds in this manner due to theunnecessary additional capital and operating expenses that would beincurred.

While the disclosure includes a limited number of embodiments, thoseskilled in the art, having benefit of this disclosure, will appreciatethat other embodiments may be devised which do not depart from the scopeof the present disclosure. Accordingly, the scope should be limited onlyby the attached claims.

What is claimed:
 1. A process for producing C5 olefins from a steamcracker C5 feed, the process comprising: reacting a mixed hydrocarbonstream comprising cyclopentadiene, linear C5 olefins, cyclic C5 olefins,and C6+ hydrocarbons wherein cyclopentadiene is dimerized to formdicyclopentadiene; separating the reacted mixture to form a firstfraction comprising the C6+ hydrocarbons and dicyclopentadiene and asecond fraction comprising the linear and cyclic C5 olefins and C5dienes; feeding the second fraction and hydrogen to a catalyticdistillation reactor system, wherein the second fraction is introducedintermediate a first catalyst zone and a second catalyst zone;concurrently in the catalytic distillation reactor system: separatingthe linear C5 olefins from the cyclic C5 olefins and C5 dienes containedin the second fraction; and selectively hydrogenating at least a portionof the C5 dienes to form additional C5 olefins; and recovering anoverhead distillate including the linear C5 olefins from the catalyticdistillation reactor system; recovering a bottoms product includingcyclic C5 olefins from the catalytic distillation reactor system;feeding a saturated hydrocarbon diluent to the catalytic distillationreactor system; determining a concentration of the saturated hydrocarbondiluent at one or more column elevations; and adjusting one or morecolumn operating parameters to maintain a set point concentration or aconcentration profile of the saturated hydrocarbon diluent at the one ormore column elevations.
 2. The process of claim 1, wherein the steps ofreacting the mixed hydrocarbon stream and separating the reacted mixtureare performed concurrently in a low temperature/low pressuredistillation column, reacting the cyclopentadiene to form a dimerizedproduct comprising dicyclopentadiene, and fractionating the mixedhydrocarbon stream to form the first fraction comprising the C6+hydrocarbons and dicyclopentadiene and the second fraction comprisingthe linear and cyclic C5 olefins and C5 dienes.
 3. The process of claim2, further comprising operating the low temperature/low pressuredistillation column in liquid continuous distillation operation.
 4. Theprocess of claim 2, wherein an average residence time in the lowtemperature/low pressure distillation column is in the range from 0.2hours to 6 hours.
 5. The process of claim 4, wherein the averageresidence time is sufficient to allow for greater than 90 wt % of thecyclopentadiene to dimerize.
 6. The process of claim 2, furthercomprising operating the low temperature/low pressure distillationcolumn at a pressure in the range from about 15 psia to about 85 psia,at an overhead condenser temperature in the range from about 90° F. toabout 150° F. and at a reboiler temperature in the range from about 155°F. to 300° F.
 7. The process of claim 1, further comprising: purging aportion of the bottoms product; reacting a remaining portion of thebottoms product in a total hydrogenation unit to convert the cyclic C5olefins to cyclopentane; and recycling the cyclopentane to the catalyticdistillation reactor system as the saturated hydrocarbon diluent.
 8. Theprocess of claim 1, wherein the saturated hydrocarbon diluent comprisesone or more hydrocarbons having a normal boiling point of at least102.5° F.
 9. The process of claim 1, further comprising feeding theoverhead distillate from the catalytic distillation reactor system to ametathesis unit and converting the linear C5 olefins to propylene. 10.The process of claim 1, wherein the overhead distillate comprises lessthan 2.5 wt % cyclopentene and wherein the second fraction comprisesless than 0.5 wt % benzene.
 11. The process of claim 1, wherein anolefin recovery, measured as moles linear and branched C5 olefins in theoverhead distillate divided by moles linear and branched C5 olefins anddienes in the mixed hydrocarbon stream, is greater than 83%.
 12. Theprocess of claim 7, wherein the reacting step is performed in adimerization reactor and the separating the reacted mixture is performedin a fractionator, the process further comprising: operating thedimerization reactor at a pressure in the range from about 130 psia toabout 170 psia and a temperature in the range from about 210° F. toabout 250° F.; operating the fractionator at a pressure in the rangefrom about 15 psia to about 85 psia and at a condenser temperature inthe range from about 97° F. and 213° F.; operating the catalyticdistillation reactor system at a pressure in the range from about 60psia to about 240 psia and a reboiler temperature in the range from 220°F. and 320° F., and a hydrogen partial pressure in the range from about1 psi to about 25 psia; and operating the total hydrogenation unit at apressure in the range from about 220 psia to about 300 psia and at atemperature in the range from about 200° F. and 260° F.
 13. The processof claim 1, further comprising partially vaporizing the second fractionprior to introducing the second fraction to the catalytic distillationreactor system, wherein the partial vaporizer is operated at conditionssufficient to vaporize between 5 wt % and 95 wt % of the C5 dienes. 14.The process of claim 1, further comprising separating the overheaddistillate to recover a product fraction comprising linear C5 olefinsand a recycle fraction comprising cyclopentene.
 15. The process of claim1, wherein the catalytic distillation reactor system has at least threereaction zones, including: (a) a first reaction zone disposed below aC5-olefin containing stream feed elevation and containing a nickel-basedcatalyst; (b) a second reaction zone disposed above the C5-olefincontaining stream feed elevation and containing a nickel-based catalyst;and (c) a third reaction zone disposed above the second reaction zoneand containing a palladium-based catalyst.
 16. The process of claim 15,wherein the nickel-based catalyst comprises from about 5 wt % to about30 wt % nickel.
 17. The process of claim 16, wherein the nickel-basedcatalyst is disposed on a diatomaceous earth support, has a BET surfacearea in the range from about 20 m²/g to about 18400 m/g, and has a porevolume in the range from about 0.2 ml/g to about 0.7 ml/g.
 18. Theprocess of claim 1, wherein the palladium-based catalyst comprises fromabout 0.2 to about 1.0 wt % palladium disposed on an alumina support.19. The process of claim 1, further comprising: determining a density ofa liquid fraction at one or more elevations of the catalyticdistillation reactor system; and adjusting one or more catalyticdistillation reactor system operating parameters to maintain a set pointdensity or density profile at the one or more elevations.